It depends on what you mean by "mash hydrometer". I would think all of use have a triple scale hydrometer and use it often. It tells you where you are starting out and when you're done, at a minimum.
If you are talking about a hydrometer used to measure alcohol from the mash in a distillery, you're on the wrong site. An alcohol hydrometer would not be of any use to beer brewers since they generally only go down to ~19% alcohol. Even my highest octane beer hasn't ever been close to that.