The only reason to stick an aftermarket rib on a gun is to improve function; I can consider that valid. And Simmons does good work. However, as to adding value as in recouping the cost-of-service plus cash-in-hand, when you get your gun back from, the whole will have been reblued with all the attendant buffing wheel polish deemed necessary to get the job done. Tough sell.
How does an after-market Simmons rib improve the function of a Model 12 pumpgun? Will it "shuck" a tad smoother with that ladder-like rib on top of the barrel- on a field gun, all they do is collect dust and grit and bird feathers apres the hunt. On a pre-mounted Trap gun, yes- worthwhile, as trap shooting has been described as "rifle shooting with a shotgun". I haven't shot a round of registered trap-16 yard rise- in years, but the 1948 M12 Pigeon Grade Trap gun I inherited would be a real test on British driven birds, with the Ken Davies style of mounting and tracking incomers- But I'd like to try it with one of my field grade 12 Model 12's sans rib-- whole 'nother ballgame, IMO anyway.