Whether or not an intumescent coating, or even a thermal or ignition barrier, is needed often depends on the type of spray foaminsulation that builders use. Many closed cell foam sprays are already sufficiently fire resistant and need no additional barriers. Ultimately, whether or not you need an ignition barrier or thermal barrier varies depending on location and materials. You should check with your local code official to ensure that your insulation work is up to code. Spray Coating
I guess I'm saying all of these products are good, they will complement the work you do on your car if you're willing to put the time into it. And it will make it easier to maintain the next time you wash your car. If you don't clay and polish your car, don't expect super slick results. If you put the work into it, when you spray the car down with water, use a soap wash, rinseless wash, it will still shiny after you put any product on it! Don't get caught up in the SIO2 hype, just spend what you're willing to pay for the product. You'll be happy with any product.