I guess it depends on your cover. If you are shooting over a birm or a wall, you woild have to expose more of yourself and your rifle. Then again, to gain the benefit of aimed fire you are going to have to expose your head to some degree. Moving around a corner it should make no difference. I would imagine your light will be much harder to manipulate from your position than mine. You will have to switch your light on and leave it on constantly, or hold your rifle in what would appear to be a very unnatural position. I can freely manipulate the light with a standard grip of the handguards.
I also look at this set up as more of a home defense set-up. When you look at how most tactical weapons are setup by law enforcement i.e. SWAT teams, the light is often on the bottom of the weapon or at the 5 or 7 o'clock position. You will see lights positioned like that on MP5s frequently. Anyway, this bracket offered two positions for mounting, either 12 o'clock or 6 o'clock, the option did not exist for this mount to go to 11 or 1.