Iodine is ineffective against Cryptosporium but is effective against Giardia. Check out "Water purification" under "water procurement" in Doug's "Gear and Equipment" reviews.

It comes down to quality vs quantity. Yes, MP1 might be a tad more effective, but I can get 3-4 times the number of iodine tablets in my mini PSK than I can MP1. And when I hike, I carry Katydyn's Hiker water filter. (my PSK is geared to be a backup to the standard contents of my pack, the survival situation I personally plan for is getting lost/ SHTF in a hiking/camping/hunting situation. Being in the military, I can't really "bug out" when a disaster strikes, better yet, I will be assiting those who haven't bugged out. So that is the compromise I am willing to make.)