They are really flexible. 390 are more of an all mountain bindings. They aren't a pure jib binding. I haven't heard a lot about them, but the little I did was pretty good. I don't think many people ride them, there may be a reason for that, there may not. Do you have your boots yet?
Im all for having fun, showing your tits and getting fucked up on a river float but it can be done without being a pig.