As a guy who owns, shoots and hunts with hammer guns in 10, 12, 16, 20 and 28 gauge, I say go for it. You seem to have covered all the major points. Ted likes Darnes (as do I - have two), so it's not as if he's not gone down his own rabbit hole with out of the ordinary shotguns.

I have not been particularly successful in cocking the hammers upon a grouse's flush, but I'm not particularly successful killing grouse with any gun. The only one of my hammer guns I'd try to hunt grouse with is my SIACE 28 gauge and that only because it has a tang safety as well as hammers. The others include two British (10 with damascus barrels; 12 sleeved with fluid steel barrels); one pre-war Austrian (16); and two modern Italian (20 and 28).

Don't forget that you can probably have the stock bent to move cast off to neutral or cast on. I suspect Mr. Hoyt could tell you which of the guns he's offering would be good candidates for such an adjustment.

Looking is half the fun. Hope you find one that suits you.