Not that rare, but still quite desirable for French C&V bike owners that want to do full French builds. Even better if it is BSC threaded, as the French bikes eventually got out of French and Swiss threading towards the mid 80's and it will also work for most other non Italian or French sized/threaded frames.... Even better yet if this BB happens to have a Ti spindle, as those go for a lot of money. A 118mm spindle length is also most popular as that 8s the spindle length to use with most C&V Stronglight double crankset.
Only minor issue I had with these BBs are the 8 notched lockrings. Not that easy to find an 8 notched spanner for these as most out there are for 6 notched lockrings. Claw wrenches would usually work, but you always run the risk of it slipping and jumping off, ruining the notches in the process...