I also take GB-3, but I find that I can only take 1/2 at a time otherwise I get a very stimulated, anxious stomach. They are very strong enzymes, and I have no doubt in my mind that they do kill some critters in the meantime.
Lots of people on this forum have had success with NOW super enzymes. I've also heard of some with very poor digestion taking the NOW enzymes and the GB-3 together to cut the expense of having to take high doses of GB-3.
Personally, I take the amount of GB-3 that I can handle, but I still end up with indigestion and bloating. I call it the "food baby" because sometimes it looks like I'm pregnant!
I'm planning to try the NOW enzymes. They are pretty cheap ($8 from Swanson's) so I figure I don't have too much to lose. If they do any good, I'm going to try and combine them with the GB-3.