During our last trip in late February we visited Leverick and saw no issues arise with BB. We anchored at the far end of the mooring field opposite the fuel dock so probably wouldn't have noticed in any event.
We went to Anegada the next day and spent two nights. We had the closest FCFS ball near Anegada Reef and Potters, so we had the BB's all around us. There were squatters each day. On the first day the crews were off the two squatting boats (traveling together) and it took a couple of hours to get sorted, but I don't think there were any harsh words - just frustration.
On the second day there were two squatters again (different boats than on the first day). One boat moved immediately after being told they were on a reserved BB, no drama. The second boat initially refused to move as the folks with the reservation circled through the mooring field 6+ times. There were many harsh words going both ways before long. Eventually a young lady came out on a dinghy, spent several minutes talking to the crew of the squatting boat, and finally the boat moved to allow the reserved boat to take the ball. The bigger problem was the squatting boat moved to our port side and anchored (after numerous failed attempts) in an untenable position. A couple of Sunsail captains that were leading a flotilla finally convinced the skipper to move, again after lots of back and forth. It became quite a spectacle, with folks riding by and hovering around in their dinghies to watch.
The incident on the second day kept us on our boat a couple of extra hours that we would have normally spent ashore. However, the entire situation left us feeling very uncomfortable about leaving our boat. Once again, everything was eventually sorted out. The second incident was all the talk at the bars that evening and caused quite a few folks to voice their frustrations. I don't think BB is to blame, it was the antics of the skipper and crew of the squatting boat. In February, at least, it didn't seem many people understood the rules.
I haven't used BB yet, but I still might consider it. However, if I have a choice I will try to avoid taking a FCFS mooring or anchoring near the BB's.