I guess I would focus more on what product you're going to be confident trusting your life to in a survival situation.

A bunch of us have used the MP1 tab's from Katadyn. They seem like they are well respected by people with a lot more knowledge than I have. I didn't even know about them until I read about them on this site, which is weird, because I've been carrying a Katadyn Guide water filter for a long time in my pack.

That's one of the great values in coming here, to this forum, and having the ability to find out what "really works" rather than just getting marketing hype. With some things, I worry about cost. With water being one of the most basic essentials I need to survive, I worry more about getting the best purification tablets, rather than the ones with lower shipping cost. I can find much cheaper water purification tab's at the local Army/Navy store, but, I carry the Katadyn ones. Ok, off my soapbox.