Has anyone here tried these cepex ball valves? They're real smooth and seem to have much finer adjustment than the cheap ones at lowes and home depot. Plus I like that they are already integrated with the unions. I'll be leaving the little mini ball valves attached to the jumbo reactors too. Never had a problem with using those for adjustment in the past either.
To be fair I haven't tried the cepex on a manifold so it might very well do the job for you. But honestly, a course adjustment on the gate valve -- say, 1/8 turn -- is still like 1/50 of a turn on the ball valve!