I spent four days in the backcountry with the SteriPen and if the proof is in the pudding, then this method of treating water passes with flying colors; no one got sick. There are really two reasons I gravitated toward the SteriPen: 1) size/weight; 2) shelf-life. The first speaks for itself; the SteriPen is lighter and packs smaller than a filter. As for the second, perhaps a little history is in order. It's been about ten years since my last backpacking trip (kids, new jobs, plenty of distractions...). Back then, I had one of the top-rated filters out there, the Pur Scout. When I was planning for my latest trip back into the wild, I wondered about whether my filter would be OK after years and years of storage. So I figured I'd buy a new cartridge, just to be safe. Of course, I came to find out that Pur got out of the hiking filter business, which they appear to have sold to Katadyn. Katadyn sells a filter that seems to fit the Scout, but it's a bit different (no iodine resin?). This all gets me thinking: will a filter purchased today be "serviceable" ten years from now? Designs change all the time. How long will replacement cartridges be available? Given that uncertainty, the SteriPen was attractive. After ten years of storage, there won't be any doubt about the soundness of the SteriPen's functionality (like there would be with a paper or ceramic cartridge filter). Either the light will turn on (and I'll know it works) or it won't. No "well the cartridge seems OK, but it's hard to say..." and then the inability to buy a new cartridge. I like the certainty the SteriPen promises in this regard. So back to the SteriPen itself. I used the pre-filter and the pour-through method. The sequence is a bit tedious, but after a few times, it's no big deal. Short cuts, including the submersion method, would no doubt cut some steps and make things quicker. When it comes to treating water, I'm pretty anal, since the price for sloppiness can be pretty steep. Your threshold might be different than mine. One of my backpacking partners brought his brand new ceramic filter on our trip as well and after one day of filtering, his filter was reduced to a trickle and thus required cleaning. There are two points to make here: 1) there's none of that nonsense with the SteriPen (a good thing); 2) with the SteriPen you don't "filter" the water, so you drink the "minerals" (an indifferent thing, but a difference for sure). My only niggle with the SteriPen has to do with the pre-filter, the threads for which might be a little "soft." Mine got buggered up right away (maybe I overtightened it--which is definitely possible--or cross-threaded it). Not a huge deal--it still works fine--but a little better (over)engineering might make the pre-filter idiot-proof.
I gave the SteriPen a four star rating simply because I have only one backcountry experience with it. In reality, it's probably a five-star product. Don't hesitate to pick one up for your next backcountry excursion.