I have fitted rifled tubes into standard and thin shotgun barrels to allow the use of slugs, and then convert to turkey hunting, for example, and helped the shooter get double duty from a barrel with sights or a scope attached. That works out to be cheaper than 2 barrels, 2 scopes, and so on.
One guy used a red-dot scope with no magnification to shoot Federal hollow-base cheapo slugs, and had the holes touching or overlapping at 50 yards.
His buddy had me fix his A-5 to have the same red dot and rifled choke, and shooting the same slugs, told me he was getting 4 to 5" groups at 100 yards. That is with no magnification, and a gun with a barrel that strokes back and forth, each shot.
When I talked to the manufacturing engineer at the tube mfg. company and told him of these results, he stated that it would have to be considered at the upper limit of what their tubes could be expected to deliver. You would have to figure that at 100 yards, that the movement of the barrel and the lack of magnification would cause at least a couple of inches in variance, all by themselves. Nobody with typical iron sights would do as well as they would with a magnified image in a scope, and a red-dot would provide similar results.
Do not expect that a rifled tube would be the ticket for high-velocity sabot slug types, though, but would work for almost all of the other types.
When I did a conversion of slug and turkey choke for a Beneli SBE, with a Leupold scope, I figured that the owner saved over $600 compared to a second barrel with scope and special work.
Read my other posts.