SB,
Before you buy a robot, I just want to make sure what you are seeing is actually dirt or debris, and not algae... Can you sweep this into a pile or at least be able to touch it or feel it...? If when you sweep it just sort of goes "poof" in a cloud and you can't feel it, it is most likely algae, which of course not a cleaner problem..
I have a couple S200's and have been impressed so far.. This is the base model, which works well for me, as I don't need all the bells and whistles.. It comes without a caddy and only has one cleaning cycle of two hours.. You can have it come on each day, every other day, or every third day.. The S300 and 300i have additional options. for a lot more money, of course...
The electrical cord to the robot is low voltage so there is no danger issue. The cable floats, so I see no reason for any overhead floats..
I bought both of mine from Margaret at Marina Pool and Spa for $700 bucks including 2 day shipping and no tax.
Thanks,
Jim R.