New pool owner here, closing in on a year now. I started off with a Pentair Rebel and it does a decent job for the most part. The drawbacks in my opinion are the fact that it will pretty much stay in the pool all the time. It's a bit of work to remove and put away so I tended to just leave it be. More importantly, for me to successfully run the Pentair, I had to keep my RPM at 1950(350ish Watts) which allowed some skimming action still along with moving the cleaner. Also, all the debris goes straight to the filter and will increase your cleaning.frequency.
In comes the robot. Drop in, plug in, walk away. First use I couldn't believe how much I picked up and that was with the Pentair in there still, mind you the pool looked clean to the eye. Was very impressed and immediately removed the rebel from service!
I now run my RPM at 1450(150ish Watts) which saves a lot of power useage. Robot takes a swim twice a week and is removed after each use, and the pool is actually cleaner.
I won't go back to a suction cleaner after having had this now, I'm sold.