There are two types, the ones that have a "barrel band", and the other style, which uses allen screws that attach to the front sight for support.
The style that uses the front sight are of course full length, and run from where the rear sight used to be, to where the front sight is.
The style that uses the barrel band isn't full length, so barrel length wouldn't really make a difference, as long as it has a barrel to attach to.
Both have their strenths and weaknesses.
The barrel band style slightly mars the barrel right in front of the frame, on the right side.
The full length style mars the front sight where the allen screws clamp to it for strength.
I prefer the classic short b-square "barrel band" style.
Once removed, both styles leave their mark.
On longer barreled guns, the full length style has more attaching options fore and aft, and you can sometimes use 3 or even 4 rings, if that's your deal.
Be warned, you may have to aim a little low at close ranges , but at 50 or 75 yards, it's right on. (Mine are all sighted in at 70 yds.)
The full length style wins the beauty contest.