I tried a similar product on the piston crown 25+ years ago on an aircooled '84 KDX200.
No noticeable difference. Unfortunately, it did not receive a long term test as the motor melted down when I encased it in mud during an enduro. I rebuilt with a 240 kit and an unpainted piston. Never used paint on a piston top again.
My personal opinion is that there are no real gains to be had in painting the piston. Since the paint maker has never tested it in your application, there are unknown risks.
I'd put the money as a downpayment toward something that will make a real difference, like a fresh set of high quality tires.
As for painting the pipe, that paint would be great for touching up a stock pipe. But I think it is going to be difficult to get a nice uniform finish from a rattle can on an FMF pipe. Steel wool and WD-40 are what many use to freshen up their FMF pipes, but it never seemed worth the effort to me.