I've been using the Adventurer for a couple of years now and have been impressed, simply on the grounds of ease of use. It's just so much quicker and less complicated than most filters or chemical additives. I've not had any problems with damage or faults, but then I tend to be pretty careful with gear. It's also done its job, in that I've not had any dodgy gut problems, but then it's mostly been used in the hills where there shouldn't have been many potentially harmful bugs. However, it's also been used a couple of times in lowland areas where I wouldn't have fancied the water otherwise.
The batteries seemed pretty consistent to me, but they're not that easy to get hold of and can be pretty expensive. It's worth stocking up with a few over the 'net, which lowers the cost a lot. A spare set of batteries isn't heavy to carry.
I went for years without treating water at all in the UK, but then a friend of mine suffered really bad guts after drinking a couple of times from a stream at about 700m in the Gorms. Other than that we had pretty much the same food and drink for several days, so it just made me think I'd rather be safe than sorry. The Steripen seems to meet my need for such an insurance policy very well.