Have not owned a .54 smoothbore. If it is a shotgun style round barrel it would possibly be good for ball & upland game. If it is a 1" octagon barrel it will be very muzzle heavy & IMHO not a good upland game barrel. I do have 2 old original doublebarrels, a 24 ga & a 16 ga shotguns & both are round smoothbores & they both work great for quail hunting & pheasants of close range. (I shoot 1/2 oz shot in the 24 ga & 3/4 oz in the 16 ga)
So if you are just wanting to shoot RB I would say go for it. But for turkey, upland game, etc. I would not buy it if it is octagon. You may kill a turkey with it, but the bore size greatly limits the amount of shot you can shoot from it & if it is open choked then the range will be quite limited to obtain a good pattern most likely unless you use wads & build an adequate wad to hold it.
Course if it is real cheap, buy it & have another toy to play with...