We've owned one of these cleaners since our pool was new in 2007. It has some quirks but can do a pretty good job. Here's what we've experienced:
1. It gets stuck. When it's working well, it scoots all around the pool floor. Depending on how you set the adjustment it will make tighter and tighter circles. But it will get hung up on the side cove. I think what happens is it rides up the cove a bit which lifts it off the bottom. There's a brush mechanism that rocks back and forth to provide locomotion and cleaning action. Once that brush lifts off the bottom, everything stops. This might be pool-dependent depending on how your cove is. Ours is high density foam - wedge shaped.
2. Keep it Clean! This is important not so much for the brushes but for the swivel connection. (the black part that the hose connects to) This seems to get crusty if it's in the water too long and sometimes needs to be forcibly rotated to clean off any accumulation of crud. It seems more like chlorine or other chemical that forms on the part. Not sure why. This will also make the unit stall in place when it can no longer spin and turn.
3. Watch the vacuum! There's a fitting that goes between the short hose provided and the main filter hose. This thing has a rubber cap that's slit like a pie and it allows water to bleed in (I suppose) when the suction gets too high which could stick the cleaner to the pool floor. I think it also allows relief should the cleaner get plugged up. The problem is it will often get pushed to the surface depending on how coiled up the hoses get. We solved this by attaching a small weight to it with a nylon tie wrap; Just enough so the fitting wants to sink.
4. It takes time. Since the operation of the unit is completely random some areas get cleaned again and again while others aren't gone over once! Given time, it will get to the entire pool, just don't start it an hour before a pool party and expect the pool to be fully cleaned. We typically just let it run all the time except when we're in the pool. (Which probably contributes to item #2 above. haha) It's easy to just push it around to areas that get missed though, so, not a big problem really.
Overall, it's a lot easier than manually vacuuming!