Black locust is one of the most stable of woods once seasoned. It would be both terrific and ugly as the devil for a bench or over the log gun. Honey locust is not in the same league, just as silver maple is not sugar maple. Black locust has no interesting grain or color. As said above, it makes great bows when carefully crafted.
I don't find it that hard on tools but then again I work a bit of Osage orange. My draw knives and scrapers and spokeshave a hold up pretty well on all these woods. That is different from other folks experiences so am not sure what's up with that. Of course all that work is with the grain on a bow and working cross grain would challenge an edge with an angle intended for most hard maple. It would take a long time to do any inletting on black locust. You'd be lucky to be able to stab more than a 64th" deep each pass. We used black locust as fence posts on our farm and most of the time could not drive a staple straight into the wood. It would end up bending over.
Most odd woods were not used for gunstocks for good reasons. Gunsmiths wanted to use wood that was abundant in good sized logs, had the right density, work-ability, toughness, stability, carve-ability, and beauty. Black locust fails on abundance in good sized logs, density (too high), workability, and beauty. I suppose it could be carved but it's plain as poplar.