For the sake of honesty, I'm just going to come right out and say it: I'm not sure how well this protects my hair against heat damage. How, you might ask? Well, my whole head has been dyed (which causes slight damage- I use an ammonia free dye though), and the very bottom pieces of my hair are, underneath the dye, bleached and have sustained chemical damage from that which I am still growing out. I do use heat tools, obviously, but only about once or twice a week and I don't use a blow dryer.
Therefore, determining how much damage comes from heat and how much comes from bleach and/or dye is almost impossible, unless you're going over your head with a microscope and a fine-tooth comb before and after styling (ain't nobody got time for that). Also my hair is naturally spiral-curly and curly hair sustains dryness, leading to damage, pretty much just from existing, sadly.
So, I can't speak 100% to the heat protection this provides but I CAN say that I've used this continually for about two years and my hair is finally growing. It might be me growing out the bleach, or this, it's probably a combination of factors to be honest.
I never EVER go near a heat tool without immersing (I mean covering every single strand with this until the hair is practically wet) my head with numerous sprays of this, then brushing it through. After its dried I go in with the tool. It dries almost instantaneously after being brushed. It leaves NO residue. The smell is not bad and not good and disappears within milliseconds.
This is awesome for several reasons: dries fast, sprays evenly, doesn't stink, doesn't make hair sticky or dry, and I actually think it helps hold whatever style you choose to do your hair in. It makes my hair look a bit glossier when I straighten it, but it's also weightless and dries to seemingly nothing.
The packaging is no fuss and sprays out evenly, and has a "lock" setting so you can bring it in a gym bag or whatever and not worry about it spilled everywhere. When it gets to the very bottom of the bottle, it no longer sprays out and I remove the top and pour it in my hands, and run it through my hair that way. Not a big deal.
Finally, the price. You get a good amount of product for $5 and seemingly 95% of people have had a good experience with this, so obviously if you're looking for a heat protectant (which is an essential item if you're using hot tools, on the same level as conditioner or sunscreen) this is a great place to start. I have had nothing but positive memories from using this and consider it my go-to heat protector, as do many others apparently!