The Vac-Clamp is a nice product for Milling machines and CNC routers where the substrate to be machined is non-porous. It's a well-made product with many uses.
Any hi-vacuum/low CFM setup, such as the Vac-Clamp, or systems that use HVAC style small rotary pumps will not be adequate when machining a porous substrate such as wood. In this case, I have found that a regular Shopvac, while putting out only 3" of Hg (mercury) and over 100 CFM, gives excellent results, in combination with a purpose-built plenum. The high CFM/Low Hg" is suitable for a router. My current Shopvac, a Fein Turbo III, puts out 7.3" Hg and 126 CFM...I thought it was going to suck the blood out of my hand the 1st time I used it!!!
It is probably the best bang for the buck as far as a vacuum source for CNC routing goes and it gives me twice the suction as my Ridgid. Gasketing is just as important as your vacuum source. I use AllStar spoilboard gasketing...and it makes all the difference in the world on small parts.
-Brady