I've never used the First Need. But I have a Steripen. It has always worked great (at least I've never gotten sick after drinking water treated by the Steripen), but I haven't used it on water where toxic chemicals were a concern. The one drawback is that it has to be used on clear water only. Any sediment in the water degrades the effectiveness, so I end up carrying a filter anyway. The nice thing is that it eliminates the need for chemical treatment and the nasty taste that some of the chemical treatments leave.

I do have to give Steripen kudos for customer service. I bought my Steripen on a Friday and I was leaving on a camping trip Saturday afternoon. When I got it home and tested it, the unit didn't work. I called the company and explained my problem. I bought the last one in the store so it wasn't possible to exchange it. They shipped a new unit to me overnight, and told me not to worry about returning the defective one until I returned from the trip. No questions asked. They paid shipping both ways, and they trusted me. Don't see that too often. I don't have any affiliation with the company.