I also bought one a few years ago, for 2 cats. Definitely expensive, especially going for the litter robot 4 over 3, but was told by friends' the 3 was somewhat loud and made their cats nervous.

Honestly have loved it. Allowed me to go on vacations with less worry about sitters cleaning the box well, or overuse between visits. One cat especially does not like to cover his mess, and the LR4 has spoiled me and him to allow his lazy habit to persist.

Definitely very expensive, but Very worthwhile for me and knowing laziness/busy times won't affect the kitties. And of all the reviews, litterrobot seemed to be the best, and most reliable.