Two adult cats here. We had a Litter Robot II for years, and now a Litter Robot III for maybe going on two. Being the one in our family stuck dealing with litter, I don't regret spending the money although it did seem painful buying the first one. Before we had a litter robot, dealing with litter used to be a daily or twice daily task, now it's an easier task twice a week.
I use two of the flat-type cardboard scratch boxes set side by side in front of the unit. That catches just about all the litter that is stuck to paws as the cats jump out.
The unit uses 13-gallon trash bags. Seems like a waste by volume, but it needs bags with that circumference opening. On weekly trash day, I usually start by swapping out the litter bag, and then walking around the house, emptying small trash cans into the used litter bag. We have a small grass yard. On mowing days, I also swap out the litter bag and dump the grass clippings into the used litter bag. So, I'm not really using any more plastic than I would be without the Litter Robot.
If the Litter Robot says it's full and I'm busy, I just shake the tray in and out a few times and that'll usually buy me the rest of the day before the bag needs to be changed.
One thing I've noticed about the Litter Robot III is that it can become off-balance. It has a triangular foot pattern, with the single foot in the rear actually being the weight sensor. As the unit cycles, the sifted litter is held in a cavity on one side of the drum. If the litter is old and gaining weight from dampness or whatever, sometimes the unit will lean over a bit when the litter is off to that side and the unit shuts down. Pressing the reset button apparently does something to reset the weight measurement; as long as I remember to press reset after refilling litter when ever I do, the unit does great.
For one of our cats, it usually gets out of the unit and sits in front of it, watching it until it cycles 5-7 minutes later. When the cycle completes, the cat walks away.