I haven't used one but I've researched it a lot because it seems like a good idea. From what I've found out about it, the easiest way for it to fail is to use it in murky water. Water should be filtered and clear first. Found that advice on the CDC page, I think, and they say it hasn't been tested well enough to trust completely, but the government could be out of date on that.

I'm also an electronics tech, and whether it worked or not over the long term would really concern me. Batteries tend to tarnish and make bad contact, no way to know how the thing works when the supply voltage drops because of that. Maybe the company tested it well, maybe not. UV bulbs that are supposed to last thousands of uses could fail after one, you just can't predict that. I'd really like to be able to depend on a SteriPEN but I don't think I could, yet. I'd like to see some really stressful testing of it and find out what it takes to break one.

JimmyTH