According to the manufacturers website it...
According to the manufacturers website it uses Phantom rubber not S1. Am I missing something?
Phantom is also known (officially) as Stealth Phantom, it's a non-marking version of the S1 rubber. It's just about as grippy, but now you can wear them around town/work/home wherever and not worry about scuffing the floors. An added benefit that I've found with the Phantom rubber is it has greater longevity because it doesn't wear as fast.