Like MOABs, BFBs can pressure the opponent with a high-HP bloon while gaining Bloontonium. However, BFBs are less flexible than MOABs, due to its 1 extra Gold cost. So, the BFB is best combined with MOABs to maximise mid-to-late-game pressure.
One MOAB and BFB give exactly enough Bloontonium for Obyn’s Spirit Strike.