Liked the Dynamic a lot (has split rollers and 2 motors, so it can actively turn), seems to be dead after 3.5 years. Then was considering ordering a suction cleaner to try and save some money, but FIL had the Diagnostic that he did not like and gave it to use to use (or maybe keep). It has a single motor, moves slower, keeps wanting to float and seems to get stuck in pattern. It work fine for being free, but if I bought again, I would want the split rollers.
Kind of gets old putting the robot in and out of the water, but with the suction side you would end up having to do the same if you did not want to be swimming with it.
I was basing my suction choices on the reviews / discussions I have seen here, so admittedly did not do a lot of research after getting the other robot.