Pop in to Richer Sounds and ask them, this is a whole different ballpark to a flat, static mount as it'll be subjected to huge torque when moving the telly around. This is why you don't see these generally going over 27" or so, because it takes a lot of force to hold a telly in position like that. Don't skimp out either, I wouldn't expect change from £200.
Keep in mind that these brackets are generally meant to be positioned once and left alone, moving them around will require something very sturdy.