Some frames don't have a batting roller to hold the batting while you are quilting & most of those that do are just keeping it off the floor--no tension on it because it is very stretchy. You'll end up with bald spots inside the quilt if you put very much tension on the batting.
When considering the purchase of a quilt frame; Sturdy--if it wobbles--run away from it. Portability--whether you want to leave it up all the time or have to store it--if you have to store it--how easy is it to setup & take down? How large of a machine can be put on it--is it upgradeable if I buy a larger machine?
Before sinking any money into a new frame, try to find some you can play with. You may decide frame quilting isn't your cup of tea or not really have the room to setup a frame.