What Rich said. I bought the M500 over the M400 for the Bluetooth remote. It is easier to create a program, although I just use the standard program at 3.5 hours--press the On button on the power supply to start it. In terms of "driving" the robot, for me that's little more than a feature designed for demos. I messed with it a little in the beginning, but I finally gave up on directing it. Which way is forward, back, left, and right when it is moving away or toward or at right angles to you? Sounds easy, but... Also as Rich mentioned, there is a delayed reaction to inputs. I decided that time it would take to master that skill could be put to better use. Besides that, I don't leave the thing in the pool. That machine costs too much to leave it soaking in a chlorine water environment 24/7. I run a cycle every three days or so. Then take it out, clean the filters, hose it off inside and out, including the cable, then put it back on the caddy under the patio cover to dry. After drying, I put a chair cover over the whole rig so any hillbillies peeking over the fence don't see it and guess it might be worth stealing.