a friend of mine that skates downhill swears by them. He uses them on weekend downhill runs and during "Balls To The Wall" runs. he has taken some gnarly spills with them with a bit of scrapping, but nothing major.
i cant believe how people are gobbling this stuff up and buying it like crazy. Yes it has impact hardening foam but even on the box it has "for indoor use only"
The ratings would be different depending on application. So they may be 5 stars for offroad dirt since they would slide better. But 4 or less for skateboarding as you state. Sliding is key. Also, it's called silicone... that thing that's grippy.