I have a used Mitutuyo gauge block set of unknown quality and an import set and use them just often enough to make them worth their cost. I tend to use gauge pins a lot more often to check sizes of holes that are too small for the usual hole measuring instruments. For larger holes where accurate sizing is needed I've gradually acquired used name-brand tri-mikes. Those aren't cheap, even used, but are satisfying to use. The ring gauges to calibrate them are pretty expensive, especially as I bought those new to be more certain of their accuracy. For holes between 0.2 and 1.2 inches where extreme accuracy isn't needed, I use a Starrett 700A internal micrometer.