The cover is called an Aquador. You would have to replace your existing skimmer plate with the Aquador fuse plate and then snap on the plastic lid. I bought it when I bought my pool. It does make it more convenient b/c you don't have to lower you water level. And yes you would buy a plug for you outlet. I don't think there is any real affect on the liner. Might be a bit easier on the cover b/c not as much hangs in the pool. Your should take your filter inside regardless of which way you cover the pool.
Do a search under Aquador/pool for more info.

Joe