I have been offered BBFS so any times, I lost count.
Is not something I do often, but once in a while I want the feeling of a raw pussy. it really depends on the girl.
When I do it, I try to stay away from girls who do it as a regular thing.
Once I had been seeing a girl a couple of months and when it finally happened I though she didn't do it with everyone.
Later on, I found out it was a regular offer in her menu. Since some time had gone by, I knew i didn't catch anything.
Another time I got it from a girl I was dating, I was upset, surprised and annoyed. My point? Catching and STD is not too scary since today's medicine cures and detects almost everything.