Building a new pool and trying to pick the best robot cleaner for my usage. Pool is 20x40, rectangle shaped. Vinyl Lined inground with an 8' deep end. I've looked at the S200 and it gets great reviews, both here and elsewhere. Is it a good fit for a pool as large as mine, or should I go with the M400? Which will do the best job, and which has the best filter system, as far as cleanability and ease of cleaning the filter out?