Less than marketing, much more than nothing. If you do nothing other than the wrap, there's a chance it'll work out. If you add in appropriate prep, such as removing the brush (remove anything like pine needles from gutters, remove all leaves, etc) for at least 30', then make sure everything around for another 75' is cut low, mow it down. That will really keep the heat down to a safe level for the wrap.

Also smart to keep the home itself in mind. Roofs should be metal, composite, tile, etc but not woof shingle. Gaps should be checked for and sealed so embers dont get in. Chimneys need to be screened, along with any vents (there are FD reviewed vents too, any state with a wildfire issue has recommendations).

Anyway, yeah, they do work, but it pays to be aware of all the ways to protect yourself/your home. It'll definitely improve the chances that temps will stay in a range they can be dealt with.