I use sabino moisture block. I'm a little over an inch past MB as of December (haven't measured lately as I go crazy measuring every month, and have put my foot down deciding to measure only every few months). My hair is currently in conrows. I alternate between braiding and flat ironing my hair to keep the dreaded natural knots at bay and other tangling that seems to happen). So anyways I've used Sabino to flat iron since around April/May of last year and my hair was above grazing bsl then. So I believe it works. Why? People say heat will cause set backs, and I haven't had any. I believe it's because I have a premium heat protectant. Heck, I'm on my way to WL and at the beginning April/May I was wearing my hair straight 50 percent of the time all the way until Oct. The only reason I'm braiding now, is I'm tired of having to style it and just want it out of the way. If it didn't take so long to dry and straighten, I'd probably be wearing it straight right now. So anyways to make a long story short, heat protectant does work.
Once upon a time I listened to a hairstylist that said hair doesn't need "extra" stuff, and my hair never changed lengths. Oh it grew, but it probably broke as fast as it grew because I just didn't see it. She was straightening my hair without protection. Now I straighten with protection with a flat iron, or a hot comb depending on my mood, and my hair is totally protected.