We have used several different kinds of these litter beads, and I definitely like them. No dust when you change litterbox (a big plus for me because of allergies!), there won't be as much litter tracked out of the litterbox after use, and I think they look kind of cool (at least when they are new).
We bought them for the first time after Kitty had surgery, because we had to get rid of the clumping litter she had at the time. We had no problems with her adjusting to them (of course, at that point she might not have cared what was in her litterbox because she was home and not at the vet, I'm not sure).
As to whether or not they really last a month, that all depends on where you keep the litterbox. If it's in the bathroom, then no. It will only last about 3 weeks there, depending on the humidity (if you have a fan in the bathroom it might last a litle longer, though). Although we only have one cat, we set up 2 litterboxes for her (before her surgery for a bladder stone, she would go under my desk to go potty if she was at this end of the house. I couldn't get too mad at her, she couldn't help it because of the stone, so we put a box under the desk to make it easier for her. It's now in the kitchen, and she doesn't even use the one in the bathroom anymore, but she doesn't go anywhere else, so we don't complain). It usually lasts a month there.
If you do decide to use the crystals, don't buy them from the pet store, though. I was doing that, but after several months, I found that you can get them for a LOT less at Walmart.
I almost forgot, they did help with odor control. This might be because we only have one cat, I'm not sure.
Another thing I almost forgot (good thing my husband is around) is that there are a few things you need to remember to do with these. When you scoop the feces out, make sure you stir the litter beads up (especially if your cat likes to pee in the same spot of the litterbox). when you stir it up, this helps to distribute any wet spots to beads that can absorb the urine. It also extends the life of the beads. If you do this every day, this is what controls odors. I found this out one day by accident while cleaning out the litterbox.
[Edited by Judi K on 02-19-2001 at 10:06 AM]