TC pro hunter has been one of my favorites for many years. Shot it mainly as a muzzle loader until last year and put a 20g turkey barrel on it. The three inch mag shells deliver a nice kick when shooting at a target. Hunting never notice it. Shot another 20g and it really rattled my teeth. Normal 2/3 inch shells and it is super sweet. Does the flex tech work? I think it does work but maybe not as much as all the marketing hype. Seems to me the recoil pad does most of the work: still if it was me I would buy the flex stock.
I am using this combo for coyote hunting as well. Currently with 7.5 Tss. Just recently bought some #4 and #9 TSS and will be loading my own. The Tss having more density may contribute to recoil. I also think if your shooting an expensive rife/shotgun like the pro hunter you have a nice investment. I would never skimp on accessories.