Very good, has been in use for a few months now, still feels brand new. Would buy again and recommend.
One edge is in millimeters, the other is in half-millimeters which is very useful for measurement for string spacing, string-to-fret distances, small distances like that which require this level of precision. The other side of the ruler has a conversion table between inches and millimeters, which is often useful given that there exist a handful of backward countries that, in their naivety, still use imperial units.