Having 3 female cats and not home all the time, I am a big believer in the LitterMaid LM 900. I have purchased many LiterMaids over the years and find the LM900 works the best; in fact I am getting ready to purchase my 3rd.  I have bought the newer LiterMaid models, but they just don't work that well. My last LM900 has lasted about 3 years. Recently, it just does not have the power to get over the hump to get the waste into the receptacle, or it catches and "things" go flying everywhere. Overall it is worth the cost of having to replace the LM900 every so many years, especially if you have fussy girls like mine that like a clean box.