I have recently done one, chose to go myself as have particularly challenging DS aged 4.5 with SN.
I guess, like most things, it depends what your course leader is like - ours was amazing, I wish she was my big sister although I realise that makes me sound like a scary stalker! I thought the course was great - a real insight into better parenting (for me).
There were 10 parents on our group, they were all very pleasant interesting folk - one dad, a few single parents a good mix.
We have since met up for a drink and will be trying to do so monthly.
I shout less and am much less stressed, DS has learnt that he gets to choose between doing as asked and getting praised or getting a time out for not complying or for being unkind.
It is a 'babysteps' course, first you do all about play, get homework on this etc, then you learn about types of praise, each week doing the play homework and then the praise. You get to 'house rules' around week 6, you eventually build up to time out (naughty step) by about week 8 or something.
How old is your DS?
I wish I could do the course again, I would love it if they ran a refresher course once a year.