I use a Traveler Opti Mini with no problems. Steripens need good quality batteries and some models should be stored without the batteries to prevent power drain. I use a thin plastic strip to keep the battery from making contact with the cap so I can keep the batteries inside for storage-- more to prevent forgetting or losing them.
It is an electronic device, so I carry some Micro Pur tablets as a backup. That gives redundant support and they are lighter than spare batteries. Stuff happens-- I could drop it and break it. I have had batteries fail, but that was very much my own doing. I've used two different models and had no actual failure other than the dead batteries.
But why use it in the first place? I wanted a quick method for water purification. The water is pretty good in most of the areas I hike in, but I don't want to get sick either. I normally have access to lots of water sources, so I can hike with the Steripen and carry one liter rather than two and do quick refills. With chemicals I would normally refill when one liter was gone and drink from the other, giving plenty of time for the chemicals to work.
I have a filter too and I think that is good for groups, where the weight and the pumping can be shared. I carry tablets as a backup for the filter as well. Stuff happens :)