I can speak to this - I did BBB with FSL because I could and Jim told me to do it and see where I land.
I learned that even though I CAN do it, doesn't meant that should do it; reason being, my recover suffers (I'm an 'older/advanced' lifter and I'm simply not going to down the 5000 calories I need to recover from squatting 330 pounds 50 times).
I wish that when I was lifting in my 20s that Jim had written these templates/programs back then because I know what BBB@FSL would have done for me. Now I'm almost 40 years old and BBB@FSL (in the squat) is just too much to recover from. I adjust my percentages for BBB to 55/60/65% instead of 65/70/75% in the squat - for the other lifts I can handle BBB@FSL no problem, including deadlifts, but I keep my deadlift TM around 70-75%, while my squat TM is 80-85%. Now that I wrote that, I should probably make my squat TM around 70-75% and do the BBB as prescribed.