In depth review of Fresh Step Premium Crystals cat litter. Also a discussion and comparison of other "crystal" litters that are made of Silica Gel. Silica Gel is not a gel at all but is essentially man made porous sand. Crystalline silica gel is extremely dangerous to inhale, but the silica gel in cat litters is amorphous form and not crystal form (despite the name of the litter). Amorphous silica gel still poses a hazard for inhalation though. Consumption and inhalation were discussed as hazards on the phone with an professional on Msds. Small amounts are usually no worry, but large amounts and prolonged exposure are.
Silica Gel is excellent at odor control and is a great desiccant (meaning it absorbs moisture). It will shrivel the cats poop to what I call mummified poop. HOWEVER, if there is urine that seeps to the bottom and is not soaked up because you(r):
1. Didn't have enough litter in your box
2. Didn't clean and sift/stir the litter enough
3. Litter is too old, used, and saturated
Then that urine (once exposed) will smell like a feral cat marked its territory with no burying or covering.
Concerning ALL types of NonClumping Litters (Crystal/ silica gel, diatomaceous earth, etc.) I find myself cautiously worrying about the buildup of urine over a 30 day period.