A muzzle compensator does not decrease velocity. Think about it: The bullet is in free flight when it enters the comp, having left the barrel at its max velocity,so the velocity reading is identical with a barrel of similar length up to the comp. The comp actually increases the velocity, but so slightly that it makes little difference, because gases are rushing out the muzzle in a rocket effect and hitting the rear of the bullet. If I had a buck for every hour I've spent on the range checking this with 3 different Oehler chronographs, I wouldn't have to hang out here!
In the First World War, it was found that the cal..303 bullet increased 35fps in velocity as it passed through the Lewis Gun's radiator front after leaving the muzzle, due to the rocket push. Handguns show a good deal less difference, and it can be discounted entirely.
For a while street carry comps were popular, the one for the Commander made the pistol overall the length of the GM and the GM holsters fit perfectly.
A comp is really useful with very heavy loads, as it allows the shooter to make accurate double and triple taps. However, as was mentioned above, the increase in muzzle flash may bother some shooters. It does not bother me, but on an indoor range, the crap dislodged from the ceiling above the firing point causes me concern, since most of it seems to find its way inside my collar.
