With the shorter barrel you are not giving up anything, you will gain all the others have said. Plus you will have a gun that shoots better, especialy the faster slugs. Look at any other rifled slug barrel you can get youre hands on. I've yet to see another one 24 in's long, although I think the Tar Hunts may be.
With the faster slugs the gun starts to move from recoil before the slug is clear of the barrel, the shorter the barrel the less time the gun has to move before the slug exits the barrel.