All equipment fails sometime. Whether it has batteries or not.

If you want to know how it works for you, check with the REI rental counter or friends who backpack who might lend one to you, and see if you can borrow one for a hike. Take along some chemicals as a backup if you're going on a long dayhike or overnighter.

I've only seen one of them in action; I like how compact they are and the prefilter that screws on a widemouth container. I didn't like that it requires a widemouth container, because it would limit capacity and mean multiple "pennings" to refill my 2L bladder.