If I can imagine the BM SMG to be a roller-delayed-blowback-operated, closed-bolt action SMG with roughly the MP5 form factor and firing 10mm, the difference between that and an actual MP5/10 or MP5 clone is small enough that you could just call it a BM MP5 and be done with it. It's like trying to say an AK-101 isn't a touched-up AK-74 because it has a black composite body/plastic furniture and and fires a somewhat more energetic round.
And there seems to be a contention that the BM SMG is not an MP5 in disguise, as far as I can tell.
