Crystal cat litter, made from biodegradable silica sand, is my favorite variety of cat litter. In case you've never experimented with it, crystal litters suck up any kind of moisture immediately. No moisture means no pungent cat urine smell or icky cat feces smell (the crystals dehydrate feces, which eliminates the smell). Since crystal litter was first released about a decade ago, practically every cat litter company has come out with their own version.
I'm not sure how the blue crystals make a difference, but the odor control of Fresh Step's crystal cat litter seems to be a little better (only a little because all crystal litters control odor so well) than other brands' crystal litters. The 10 lb. bags fill up a normal size litterbox well enough to make the "one cat, one bag, one month" claim realistic. However, to get to that one month, you must scoop out the dehydrated feces, stir the litter around, and occasionally add fresh litter. Stirring the litter is very important; if you don't stir it, the crystals on top will reach their maximum absorbancy and no longer soak up moisture while fresh crystals will sit at the bottom without doing any good.
The one downside to this kind of litter: when it stops working, it just stops. No warning. When crystals reach their maximum absorbancy, the no longer soak up moisture, so the kitty urine just sits there... stinking. There's no slightly stinky warning, it just happens full force one day. Again, stirring the litter prolongs its effectiveness greatly, and, unless your cat pees a lot, one bag one month one cat is about right.