I can't say I'm keen on them, although I understand why some peeps with show cars etc may want to use them .
A bloke I know at the M.O.T.station where I go has just bought one for the T2 splittie that he has restored ÂÂÂ

no expense spared.
( I'll post some pics of it up soon hopefully ,but at the moment he won't let a camera near it until he's ready to unveil it at shows )
anyway, he's been told to be careful how much he uses it as it can damage the paintwork by any movement/rubbing on the body when used and cause moisture build up .The one thing he's doing is to put felt or something like that on the underside so as to reduce any chance of damaging the paint.