I got this on a major sale at a local pet shop, and now I know why. First, you do have to keep it filled fairly high, or else the rake won't get the waste. The cat also is able to urninate beyond the rake, which forces me to remove the rake and clean out the clumps with the scooper. This is not why I bought a self-cleaning litter box.When the rake does lift up the lid to deposit the waste, sometimes the plastic receptacle lid falls loose, and it makes a mess. I wind up cleaning more around this litter box than any traditional one.It is also very noisy when running - enough to wake me up at night, and I am a heavy sleeper.