That's more correctly called a "Crown Thickness Gauge", used to measure the thickness of dental castings or their wax precursors. They're good to a tenth of a millimeter. They come in different levels of quality, but the inexpensive ones are quite serviceable for most applications. The one you showed indicates "0" when the jaws are closed, so it's going to be reasonably accurate. When I was in dental school 40 years ago, I was required to purchase one that cost about $60... and is probably no more accurate than less expensive ones. With reasonable care, they last forever.

This is like the one I had to buy. The finish is better, but it's probably not more accurate.