Stay away from the Dolphin Diagnostic. It works well for a while but they break down quickly--and, as stated above, service is atrocious. That's experience talking. Their motors are far smaller than the Blue Diamond's and that's a problem for the vacuum motor as the unit is much heavier.

Blue Diamonds do much better. Their bags work just as well but are far easier to clean. The unit is lighter and can do in 3 hours what the Dolphin does in 8.

I know Aquabots have a good rep but I've never had one.

Still, robotics are addictive! They are all fundamentally the same, originally all coming from one company--I think it was a family where they got mad at each other and started their own version.