I never noticed any difference in recoil reduction.
However, one noticed a substantial difference in patterns (tightness) using a Vang modified barrel and factory ammo back in '86.
With the advent of new "flightwad" technology and metal composition the advantage of the Vang Comp system has been diminished.
As I see it, you have to balance the amount of shooting you will do to justify the additional cost of the modification which will allow you to use cheaper ammo vs. the cost of more expensive ammo out of a factory (ish) barrel.
L