Yes - I have heard that as well - and I know that this is Therm's belief.
I thought about it.
One thing I have read from many who have them - since they cover the flash hider - they get very dirty inside. If you clean it, you have to take it on and off. And, while doing that - you'll scratch up your barrel over time... If it matters to you... (it may not)
I have one on one of my USGs and its only on a gun that I do not shoot.
IMO, its too much of a hassle if you plan to shoot the gun.
Shipwreck is correct about cleaning, from looking at it you would have to clean the gun and the fake can. Also taking it on/off every time to clean defeats the purpose of an easy to stip gun.