Mate of mine who’s a JKD instructor went to Israel for an intensive Krav course, and most of the course were Russian professional protection guys... not that they were unfriendly but they were mega serious about it.
Loads of fun apparently... fighting in a moving car, on uneven surfaces, in a plane.
Tried Krav before I started JKD... and dunno if it was where I tried it but it didn’t really do much for me... a bit too contrived in the little I did... but know people who swear by it.