The massive forward bulk(not so much weight) seems as if it would be awkward. I also was always trained to keep my light far out to the side. This would keep the bad guys shooting at your light from shooting at you.
I have never been in a situation that called for this tactic so I can't swear to it, but it makes sense in theory.
I'm not a big fan of "mounted" lasers/lights, but they do have a place. regarding weight, the M6 is probably about as light as you'll find (it doesn't add much subjectively, for me). The Streamlight TLRs have a proven track record, as do Surefires, tho' older Glocks had issues with either the weight and/or the clamping system on the SF.
For CTC, bulk & weight really are not issues.