Since it is a repeatable micrometer why not record the setting for the bullet(s) and screw the head back in to fit the box? Then when you take it out put it back to the pre-recorded setting.
I've used the Redding comp seaters exclusively for a few years now but recently bought my first Forster comp seater - the kind with the plain screw and lock nut setting. It eliminates runout every bit as well as the Redding and is a good deal cheaper so that will be the kind I buy in the future.
FWIW, once you know the tpi count it's not that hard to eyeball changes to the seating depth. E.g., 20 tpi one turn = .05", half turn = .025, quarter turn = .0125, eighth turn = .00625 etc. It's not as dead nuts accurate as a micrometer head for those last .001" changes (everybody seats to +- .001" right?
) but with just a little practice a fellow can seat long, take a caliper reading and even going down over a tenth get within .000 to .002" of where you want to be on the next try.