They've been in the leagues I do for a few seasons now and I find it really helps. You will always get those players who just don't care and will give it no matter what the punishment. But for the most part I really feel it's made a difference. Most players seem to get really annoyed with the guy in the SB and after one SB (I've only done about 4 all season) it definitely adds a lot more control, with players telling their own team to shut up and stop making comments.
One question though, what is the punishment for dissent for a substitute? Just a normal yellow?