Both.

The nature of the beast is that it is limited to angle adjustments in increments of just under 10 degrees (42 grooves on the Brooks versions).

There is a good likelyhood that the angle you want - and try to set - is NOT one of those 42 that allows the grooves to mate, so either it moves slightly into the nearest mating angle as you tighten the nut, or it mashes the points of the grooves together, and quickly becomes loose.

So unless you choose to/are lucky enough to have it work for you where it works for it, you're better off with a micro-adjust, either the Simplex style or a Record style.