Denis Dmitriev (RUS) seems to go back and forth between NJS and nylon:
Sandie Clair (FRA) uses doubles:
Förstemann (GER) uses doubles:
There seems to be a 60/40 or 70/30 nylon/NJS split among sprinters. The NJS straps are a really, really mature product. The clasp is an engineering marvel.
Also, I have weighed them all:
1 BLS strap: 32g
1 single Toshi NJS strap: 31g
1 double Toshi NJS strap: 67g