Originally Posted by Buffering
This is not complicated to answer.
1. If the extension is made by a good and reputable company such as Scattergun, you do not need a clamp to hold it in place. You wouldn't be buying *****ty parts in the first place so it is not needed.
2. If you need the real estate to put on a light and such then a combo clamp/mount from someone such as Mesa Tactical has a place but whatever you do, keep it simple and keep crap off of your gun unless it is purpose necessary. A clamp does not fall into that category unless you buy a *****ty one. Scatterguns and Vang are couple of the good comapnies, among others.
That's all you need to know right there.