I had never run in TNF shoes until I bought these for a recent 50k trail race on some pretty technical terrain in northern MN. Initially, I could not have been more pleased with the breathability of the upper, comfort of the midsole, and durability of the outsole. They seemed like everything I want in a 50k+ racing shoe. They are definitely the most comfortable trail shoe I have used in recent memory and have the comfort and protection to handle some pretty technical terrain for ultra distances.
Now for the negative... 1) The heel counter is somewhat lacking. It does a good job of holding your foot in place but perhaps lacks some stiffness to help with lateral and medial support that is helpful on longer runs on technical terrain. 2) The upper does not drain well when submerged, and really it doesn't dry from sweat that well either. The Flash Dry doesn't seem to work as well in shoes as it does in clothing. 3)The upper is not durable. I uploaded a picture of my shoes after less than 100 miles of running. 50k of it was a race under some pretty tough conditions so the wear can be somewhat discounted, but the fact remains the upper wore through relatively quickly. Hard to trust a shoe for anything more than training when the upper begins falling apart so quickly under race conditions.
That said, if you can find these shoes on sale I would highly recommend them in spite of the shortcomings particularly if you are a runner that does lots of road to trail running or runs on groomed trails. Heck, they are just cools looking and would make great casual shoes too. I will continue to use them for training as long as I am not paying full retail.