Well, I finally have my new Mag installed and set to go.
The new Mag sounds great, definitely more punch to it than my BMs had. The drum hits on Pink Floyd's The Wall album are all clean, crisp and precise. Much more pointed that on the BM.
On Nine Inch Nails Discipline, the notes have an actual shape to them, there is a buildup and a decay, not just a thwack from the drum hit. Again, I can't say the BMs sounded bad as they destroy any other sub I have heard in SQ, but the Mag truly is that much better.
On rap this sub keeps up great and still gets plenty loud for me. It definitely has less output than my 2 BMs, but those were 2 ported subs versus 1 sealed sub, I 100% expected that.
Also, there seems to be fewer peaks and valleys through the frequency range with the Mag. I am not sure if this is due to it being a sealed box or because of the Mag itself, but it's a more linear frequency response than my BMs had.
I must note however that if you are at all looking for SPL, this is not the sub for you, it can get loud, but it is not an SPL sub at all. Also, it is designed to take a Maximum of 1000 watts, it does not need 1000 watts, 500 should do fine in most cases, especially since it is only a 3 dB difference, barely audible.
In conclusion, if you are looking for a very dynamic and listenable sub, this is it, but if you want more SPL, find an old Mag V3 or an old BM, it will serve you better.