I think you'll get lots of responses, with good reason, on how Steripen and other electronic devices should always have a back up as electronics tend to go bad at just the wrong time.

UV purification, however, is excellent against all living microorganisms. Post treatment filtration with some sort of brita or activated carbon would get out most of the chemicals.

In my BOB I have a Miox pen to create mixed oxidants. Purifies, and also can oxidize chemicals. I could add a Brita style bottle to remove any residual chlorine or other chemicals.

I do like the steripen. Can't comment on the First Need purifier.

Eric