I am asking for your suggestion on what model to purchase. We are a YMCA with an in ground pool 75x50 3.5'to 5'stainless with a liner. I am looking for a robotic vac. that will clean floor walls & waterline and have little to no problems as we are a non for profit organization with a limited budget. I have looked at the models 6564,7175,5553 but am unsure the difference in these models. I also need info on the warranty and the proses of repairs. Any help would be appreciated. Thank You.