I didn't know that, I thought it was a 16 inch barrel. In that case I think it's ridiculous unless someone is using it for competition.Depends what you're doing with your carbine. The Taccom barrel only has 5.25 inches of actual barrel, the rest is a fixed shroud to make it 16 inches.
Speed games would benefit but you end up with with pistol barrel velocities and possibly lose accuracy at longer ranges.
About 20% increase. From what I've seen once you get to 9 or 10 inches the increase in velocity at 16 inches is minimal.not sure that makes a big difference though. Does the 9mm round actually gain that much more velocity from a 16in barrel over a 5.5in? I use my rifle for plinking only, so I still think it would make a cool option.