A buddy of mine has one on his Jeep. Other than putting it on being a total pain because it was figgin' cold outside. It took it about 2 weeks to fully settle. He just keeps pulling the straps tighter. He also made a piece that goes along the back pillars so help the window keep it's shape. He was worried about the sag as well.
I have had mine on since October and I love it. As long as its not too cold outside it is easy to get on. No flapping from the back window at all nor from the side windows. They fit nice and tight. It is quieter than when I had my stock soft top on. Very much worth the money.
I'm thinking of getting one too, but have a question for those of you going from a hard top to a Rampage Frameless. Do they come with the door surrounds for lack of a better term? They've got to have something to connect to around the doors correct?