Interesting thread. I only recently started to question the quality of the movement in my current test indicator (0.0005). I figure at that level, even the slightest friction is going to lead to bogus readings.
I indicate my vises using that indicator and I get them within a half. I always thought that was close enough but, on a part that flips in the vise, the error gets doubled. Make that part a foot long and suddenly, there are mismatches in machined surfaces and other anomalies. I'm starting to see why I might need more places.
How hard are they to use? They seem to have very limited range and I'm imagining that they're very jumpy until you get things almost perfect. Do you use a coarse indicator to get something close, then follow it with the finer gauge?