It does make things noticeably more quiet.
It does retain engine compartment heat noticeably better, allowing for quicker warm-ups. Getting into closed loop is much quicker thus FE and emissions are better.
Do I have temp probe test results? No. Do I have FE charts before/after? No. Still, I know it works.
Works even better with a grille block.
Material choice doesn't even need to be hi-tech. I think a large component of it working is simply in reducing compartment drafts (convection losses). On my car there is no room for anything more than a single thickness of corrugated cardboard to span the entire engine compartment. On my pickup I have the luxury of using foil faced 1" thick foam board.
P.S. I started fooling with this stuff about 14 years ago cuz I hadta commute through crap conditions kinda like this:
I wanted to be kinder to my engine, and I wanted more instantaneous defroster function at the end of the workday.