Judging by the location of his storefront, I'm assuming that Ken's work is first rate. However, I do question the basic design concept of his system.
I have several stocks with recoil reduction systems. With Ken's system your shoulder is helped but your cheek will still take full recoil. Have you considered a system where the comb reciprocates with the butt plate?
For my trap gun I have a
Shockmaster where the comb is linked to the butt plate and they slide together. On my skeet gun I have a JS Air Cushion stock where the stock actually telescopes, like the old hydro-coil stocks; but, the JS stock is all wood, not plastic. Both stocks use the B-squared air unit. These are all metal, not plastic as in some other early air units. I prefer the air stocks because of their ease of adjustment, no changing springs and/or shims as with some designs.