i have two indoor cats and i also use the crystals. we did use clumping and found it absobed well but didnt mask the smell at all. the crystals do last a little bit longer than paper and clumping, and hides the smell for longer but i found it to be not very absorbent and thats why it needs to be changes weekly (even though the packet says it should last 2-4 weeks - bollocks) my cats dont eat it either and we did change from paper to clumping to crystals fairly close together but it didnt phase them at all