We also have a 20x40 vinyl inground. We were discouraged from getting the under-diving board model and wound up with a very large commercial model. Big mistake (if anyone wants a reel that can span a 30' pool and hold up to 60', I have a deal for you).

We are in the process of working with our builder to replace this huge beast (which lets the cover freewheel right into the pool!), so I'll be real interested in hearing what others have to say.