For what you want I think they are a big waste of time.
I read some things from John Broz about them. He said they didn't do them because back angle was the same as the back squat, build your back squat and it builds your overhead squat.
Overhead squats are also limited to what you can balance therefore back squats will give you a much better leg workout than the overhead squats.
Don't worry so much about butt wink. I even read rip saying a slight butt wink is no problem. Broz was asked about it on bb.com and said don't worry about it, plenty of O lifters have a butt wink, pendlay said the same as far as I can remember.
You want big quads, focus on your back and front squat.