I just bought two front sight tower light mounts. Haven't had a chance to test them. I like them because they were simple and inexpensive. My guns tend to be pretty plain by commando standards, lol.

I suppose I should have asked BEFORE I bought them but is there any downside to using this type of mount? They seem to work great, the Surefire with dedicated mount that I am using sits in just the right spot to activate the light with my off hand thumb. The only thing I am wondering about is if mounting it on the sight tower could somehow affect my zero? Sight tower connected to the barrel etc.....

Anyone running one of these have that issue?

Any additional weight or item added to the barrel directly or indirectly will have some effect on zero and require re zeroing the weapon after installation.  As far as long range work that fact will show more than closer in.  I have my sling and light mounted on a block on each side of the sight tower on a 11.5 inch commando for work.  That said, I can still hit steel at 200 yards with the 4 moa M2.  If you want to do better than that you are always better off to free float with a quad rail and mount everything to that.  If I have to take a shot that far away, there is going to a sore sniper later on...