N.L. nailed it, the slide of the 101's is insanely controllable and nearly impossible to catch and eat shit. The 99's took a lot more effort to slide and didn't allow me to go for long periods and have that control, which was also the case with STF's. Bones STF's are like 83-84b which to me just equates to 99 duro no matter how much they wanna say it equal's 101a or higher. Just get Spitfire 101a's man, you won't regret it.