So I bought some Booster Strap Expert/Racer ( 3 stretchy bands ) mid last season but never got around to installing them. I installed them on my last outing, and ran them fully over the shell, not under the outer cuff. I had my 4th buckle set with just a bit of tension and had the Booster snugged quite tight. My boots are Atomic Hawx Ultra 110.
I found the Boosters gave me quicker responsiveness, and a more comfortable ride overall. Previously, if I had my power strap quite tight, my shins could get achy, or I'd be too upright, yet that didn't seem to allow me to flex/drive the boot and give me added responsiveness. The Boosters give me a secure interface at the top of the boot, providing better initial engagement, and the elasticity still let me drive my knees more than previously. Well worth the $45 IMO.