I have had an old "60" version for about three years and I am going to upgrade after I use up all the sani solution I have for it. Everything about this system is great! I have only ever had three issues with it.
1. the granules get tracked all over the house cause we have no carpet but I bought a matt to put in front of the cat genie to combat that.
2. It stinks when it cleans after a while of use, so i give it a good cleaning.
3. Through some unknown events a dryer sheet ended up wrapped in the impeller and this clogged it up pretty good. It was very easy to take it apart to get to the problem though, I ended up using the clogg as a reason for a thorough cleaning and then all was well.
Even with these issues I give the "60" an 8.8 out of 10! I can only assume from the other reviews that the "120" is just as good if not better.