G'day,
i´m not familiar with vintage FF´s in a particular way, but realize there´s a variety of models and movements. None of them is particularly special to BP, but all more or less "conventional" third-party supplies.
What might be more interesting may be the impression there are probably more fake or "put together" FF´s around than "real" and original ones.
Because of this, i´d personally much prefer to buy from a trustworthy source who will stand behind the watch and it´s originality.
This particularly if buying online, as a couple of problems may reveal themselves only if the pieces is seen in nature.
Cheers,
Peter