No experience but friends with cats have complained of it breaking down, not working properly, and noisy. This may not apply to all models, however. Definitely get some youtube and online reviews for different models!
Not sure what model you're considering, but I've heard concern about kittens possibly getting caught in the mechanism (worse case scenario). I had one when I brought Ickus home as a kit but his poo was so soft it was a complete mess!! Then, by the time his poop was solid the box was not big enough. I've always had the largest box I can find. Ickus used to fling so much litter, I bought him a bussing tub from a restaurant supply store. There's something about poo always stuck to the grate that I don't like with the old school automatic boxes, but there are probably better mechanical cleaning options now. Ickus used the crystal litter for a while with no problem (though he was never picky about litter). I haven't tried it with Eudo, though, since I'm thinking now that the crystal dust is more dangerous than most.
Never used them myself did look into it once but the what I heard from others was;
Get one sloppy poo and it makes a huge mess
Some have a delay so the cat never see's it remove the poo, but I know of one that out of the blue stopped using the litter box full stop, so it seems the cat went back or stayed nearby when it started to self clean and freaked the cat out
As others say they break down and don't seem to last
After that I realised that I was just being lazy and wanted something to do it for me, so never bought one.
I have a sizeable box and scoop about four times per day. Options are to get a large box, or several boxes if you cannot scoop frequently. Cheaper and more reliable options than the automatic, perhaps. Cheers!
I've used the littermaid one and they keep breaking. Last one I got only lived about a month. I've used the one for crystals too (ScoopFree) - those worked pretty well without breaking, but the crystals got expensive for me with the number of litter boxes I need, so I'm back to manual boxes.