I have seen a number of them over the years, and for the most part I consider them to be mostly shoddy constructed tools aimed at taking money away from musicians that don't know any better or taking money away from friends and family of musicians searching for the "perfect gift." I haven't seen any good quality ones that would be any better than keeping a SwissTool or something in your guitar case. In fact, I have used a variety of multitools, probably most commonly a Spirit, to repair the instruments of bands that would play at the bars I worked at, often while the rest of the band was playing.
Two things I find appalling- many musicians never seem to look after or spend much time maintaining their instruments (other than tuning) and many haven't got a clue what to do when a humbucker refuses to hum. If you want to base your lifestyle on a piece of equipment, at least know how to perform (no pun intended) basic repairs and upkeep on said equipment, There won't always be a doorman there to help you out!
While many of these market specific type tools exist, I have never seen one that beats a good EDC tool, nor have I seen one well crafted or worth the money. I'd like to, but one has never crossed my path as of yet.
In fact, the only market specific tools that seem worth having are the cycling multitools, since most EDC oriented tools don't have Allen wrenches on them. And even they range a lot from very good to absolute crap.
Def