Just don't buy a ProMag- I did and it jams the gun something fierce. There are two common factory BDM mags- one says Browning BDM on it; the other just says "9mm Made in USA" and has the 5-10-15 round holes on the back which ProMag does not. But if you're sure you're getting a Mec-Gar that's the cream of the crop. They make a lot of factory mags for FN anyway.
What I don't understand is that FN/Browning stopped making mags for the BDM and also the FN HP-DA (also called the Browning BDA-9) when they stopped making the guns and that just isn't right. They should also have parts available to the larger factory authorized repair shops like Midwest Gun Works. FN is a first class company which is why I can't understand this. The BDM may not have been quite what law enforcement was looking for but the HP-DA (BDA-9) is a really solid gun. If they'd pushed harder it may have gone over. I have a BDM and two HP-DAs because I think that much of them. (I also have a very nice Hi-Power Practical.)
By the way, in case this info hasn't been posted on this website, the 15 round BDM mags will work in the HP-DA/BDA-9 and vice versa.
Best regards,
Bill in Cleveland