Just wondering how they work? Pro's and Con's ?

I've always heard and read that they don't work but I've never tried them.

not in a dominator but i had one in a 4150 series carb. took a while to get it dialed in but once there it was easy to play with. had to keep a note book to remind which way i had last adjusted it. these days i'm too lazy to change jetting. i run super gas & have more than enough power to do the number.