I've just about made up my mind to mount my light to my FSB using the GG&G 1228HD and am wondering what the disadvantages to this set up are?  I don't see it done much but figured it was because of all the cool new ways to mount lights on rails.  I've got a 7" railed HG on my carbine but can't seem to get the light in a comfortable spot.  

As far as brands go, the GGG seems to be lower profile than the MI version...yes?

ETA: After a lot of goofing around and measuring it appears that the new Magpul rail light mount would put the light in about the same place so the question is...

Which would you use for HD/Zombie/just paranoid scenario?

I tried the FSB mount for a while but abandoned it (same mount you're looking at too). Ultimately I decided I wanted a longer forearm and to mount the light farther forward (which also helped to reduce/eliminate barrel shadowing from the light). When bolting a light to the FSB, you are essentially adding weight/harmonic variance to the barrel so your zero/impact may change. Granted, the impact change probably won't make much of a difference at any distance where you're actually running the light, but in the long run, mounting the light to the rail seemed to be more secure and resulted in fewer variables for me. That said, that GG&G mount excellent quality and is GTG... just make sure you loctite the mount.