They're legal and most of the cars have them. I'd say there's a pretty good sized contingent that doesn't use the trans-brake. I know a lot of guys that are footbraking (Bucky for example; at least the last time I saw him) or two-step off the brake pedal (Houser, sometimes us).
I personally think the cars are a little too violent off the trans-brake, but there's a lot of guys that make it work (see: Charlie Westcott) , so I can't knock it.
