I have the hard plastic Honda roof, and its great. It fit well during installation too.I don't know anything about the SATV roof; I don't they offered one when I was in the market for one.
For the SATV flip up windshield, it has two arms that are pressurized that go in and out. They hold it open when riding and going over bumps, etc. That was my question too, before I got it. But it has been flawless for the 5 years I've had it. Rock solid. Only thing is that the windshield has to be closed when trailering it. Its also super easy to close while riding, where as someone mentioned having to stop and take a minute to close the flip down windshield.
The fold down seemed like it would get dirty easier and it would break easier if something fell on it while open. But not sure about that.