Personally it has worked for me...I survived a head on collision at 80Kph on a Honda 1000 Intercepter in 1984. I went completely over the top on vehicle and slammed shoulder head first onto pavement and then slid face first 80 feet and eventually flipping onto my back into a ditch just stopping short of a culvert.
I was wearing a Simpson helmet and Hondaline no armour leathers with Leather Moto cross boots. My visor was melting as I slid with the gap created filling with road grime till I came to a stop. I had a large junk of my helmet disappear in the upper left quadrant were I first hit the pavement. My leathers looked like I went through a cheese grater but remained in tact.
I was transported 20 min lights and sirens to local hospital were I was check over and was told by doctor to buy Lotto Ticket as I walked out of Hospital under own power without so much as a scratch.
Few days later the bruises did arrive and I looked like the loser of a baseball bat fight....but no worse the wear. I was on new bike next season and enrolled in a Kawasaki race school on my new bike.
I have since lived with the credo that I can always cool off at my leisure but it sucks trying to grow new skin all summer.