I bought one of these almost a year ago and reviewed it here a couple of months ago, at which time I was quite harsh in my comments. I still stand by my remarks at that time but, on reflection, I feel this jacket worthy of a good deal of positive praise, which I've now included in more depth. This review is still likely to ruffle a few feathers but I have appreciated the honest reviews of other contributors to this site, so I would like to share my experiences as candidly as possible.

Pros:

Very lightweight

Great freedom of movement whilst wearing the jacket.

Very compressible and portable

Welded construction means very few stitched seams and therefore minimal egress of goosedown from the jacket. Also aids in water repellency and overall durability of the garment.

Very nice overal quality of manufacture (if you place the Prism Optimus alongside a Nuptse, you can thoroughly appreciate the difference in quality of manufacture. The Nuptse is well made but the Prism Optimus's quality of manufacture is in a different league and really shows where some of your extra hard-earned cash is going).

Nice large hand pockets which will (within reason!) accomodate more than just your hands. They go about 8 inches high and all the way to the centre zip.

Wonderful UPPER hood adjustment-drawcord on the rear/crown of the hood. This is hands-down the best adjuster of its type (note: specifically for the crown and brow of the head) that I have ever seen on any jacket. One pull and the hood is pulled snugly around your brow and your ears and crown. This is quite different from the drawcords one tends to see on most jackets, at the collar bone area. Both are good, and suit different purposes. If I had the opportunity to design my dream jacket, I'd incorporate BOTH systems for the hood. I should point out that the collarbone drawcords are more important, so IF I could only have ONE type of adjustment, I'd go with collarbone drawcords, simply because these tend to aid in protecting the cheeks and neck. As far as UPPER hood adjustment goes, most manufacturers tend to just sew on a crude velcro tab to the crown of the hood, which is uncomfortable in use and looks amateur and unsightly. Top marks to TNF for their implementation of a cleverly-designed drawcord here on the top-rear of the Prism Optimus hood.

Doesn't make you look like a blimp when you wear it (both due to the welded construction and due to the efficient use of down, rather than highly-stuffed).

The zip, athough, admittedly, not being waterproofed with a laser-cut vinyl protector strip, is actually superior IN OPERATION to that on the TNF Himalayan Parka (the Himalayan's zip is a pig to engage and binds when being drawn up over the chest region). This has much to do with the fact that the Prism Optimus zip utilises larger teeth than the Himalayan zip.

Cons:

The DWR coating lasts a few months at most before it becomes useless (unless you get the jacket professionally cleaned and treated regularly, which, let's face it, very few people do). In fairness, though, this criticism is true of many DWR-treated fabrics, not just those used by TNF.

If you take a CLOSE look at the photograph of the jacket, you can see that
1) there are no drawcords in the collarbone area, and
2) the sides of the hood, by virtue of the way they have been cut/tailored, do not draw in towards the chin - instead, they are cut so as to go straight down to the collar/shoulders of the jacket. Unfortunately, I did not notice this when I bought mine in the UK. The result of this horrendous design flaw is that the jacket is reasonably warm on a still day, but as soon as a breeze of as little as 10-15mph gets up, it rushes straight into the hood, past your cheeks, and down through the collar, chilling your entire body to the core and flushing out the warm body heat through the bottom of the jacket. It beggars belief that this jacket was designed with any consultation whatsoever with mountaineers! I reported this glaring design flaw to TNF Europe and instead of seriously listening to my concerns, they simply told me that I was (supposedly) 'the first person to ever mention it as a possible problem', and consequently would 'pass on my concerns' but it was abundantly clear that they thereafter considered my interaction with them redundant and satisfactorily concluded. In short, buyer beware: TNF appear to have something of an 'attitude problem' - instead of properly considering customer feedback, they apparently seek to diminish its credibility and continue to arrogantly produce products with known flaws. TNF have achieved a huge growth in market share partly because they have focused upon satisfying the demands of the fashion industry, to appeal to a broader cross-section of the general public. Their design teams are therefore unfortunately focused as much on 'form OVER function' as they are on 'form FOLLOWS function'. I had hoped that, on account of this particular jacket being marketed as part of the 'Summit Series', the design team might have biased their focus in favour of 'form FOLLOWS function', but my experience has sadly proved otherwise.

It is perplexing that they should design the rear adjuster of the hood so fantastically-well, only to utterly fail in their design of the not-quite-high-enough (and insufficiently-stuffed) collar, omission of neck/collarbone drawcords for the hood, omission of a 'halo' neck baffle (the TNF Himalayan sports one of these to superb effect), and appallingly inadequate hood protection of the cheeks and side of the neck. Weight saving and freedom-of-movement design goals do not justify these unnecessary ommissions/failings.

I also own a RAB 'Neutrino PLUS' and a TNF Himalayan, and the Himalayan, in particular, protects the neck and cheeks admirably (the Neutrino Plus has a much higher collar than the Prism Optimus, as does the Himalayan, but the Himalayan also includes a down-filled neck 'halo' baffle). The Himalayan, whilst admittedly a more serious and expensive garment than the Prism Optimus, nonetheless demonstrates that TNF DO know how to design a hood and collar properly when they feel so-inclined. I also happen to know that TNF take great pride in their 'Summit Series' product line, which, again, leaves me scratching my head over their attitude towards the above Prism Optimus design flaws.

In conclusion, this IS a nice, lightweight, good-looking jacket which is great for doing the shopping on a winters day, and if you are looking for a jacket for this particular purpose, I'm sure you'll like the Prism Optimus very much. However, for users who need a jacket they can rely on to fend off the elements on belays or mountaineering excursions, please don't believe the nonsense marketing hype that the Prism Optimus (in its current incarnation) is designed for serious mountaineering use (or on any day when there's more than a slight, chilly, breeze).If you like it, then by all means buy it (along with a neck gaiter as, quite literally, a 'stop-gap' solution) but bear in mind that you will still need to buy a more serious jacket in addition, for those days when you want to go somewhere more demanding than the high street or the shopping mall. If TNF decide to swallow their pride and modify the design of this collar/hood for Winter 2010, they will at least triple the usability of this jacket so please bear this in mind if you read this review in 2010 or beyond. This jacket has potential for fast, lightweight ascents, and for belaying duties, but ONLY IF the hood design is redesigned to protect the neck and chin properly.

For those of you wondering what the fill weight is, I don't know precisely, but I now estimate it to be approximately 290 grams. It is very marginally loftier than my Rab Neutrino Plus (the Rab is 275gm EU 750+), so, what with the TNF Prism Optmius having a lower fill power (700 US / 600 EU) but very slightly higher overall garment loft (notably on the lower arms), I reckon 290gm is a fairly accurate estimate.

It should be noted that, in the European marketplace, at least, the Prism Optimus faces stiff competition from Mountain Equipment's 'Omega' (which is welded construction 280g EU 700+) and the aforementioned Rab Neutrino Plus (I suspect the recently-released Neutrino Plus is intended as a direct and deliberate snipe at the Prism Optimus). I haven't tried an ME Omega yet but that will change within the next week or so, at which point I'll repost. In the meantime, the Neutrino Plus is very similar indeed but scores over the Prism Optimus with a much higher (and superior) collar, along with proper neck/collarbone hood adjuster cords (albeit missing spring-loaded grips), and a stiffened peak to the hood. However, the Prism Optimus wins back some points by being very marginally loftier, including a little Primaloft insulation on the torso side of the handpockets (the Neutrino Plus lacks this detail, so one's hands tend to get cold if the jacket is not zipped closed around the torso), and by using welded construction. Both jackets are extremely comfortable to wear, being lightweight and allowing excellent freedom of movement. As a purely secondary observation, both jackets are rather good looking, as down jackets go, which is a pleasant bonus.

Despite my design criticisms, I remain fond of my TNF Prism Optimus and would absolutely love it, if only TNF would redesign the hood and collar. In all other aspects, this is a great jacket and IS, as TNF claim, very durable in it's construction, despite its light weight. It's SO close to being a classic, so come on TNF, raise your game for 2010 and you'll have a winner on your hands...!