I am disappointed that the only thing SVS seems to discount anymore is these NSD subs!
Mechanically, they are very potent subs for the cost (esp. when discounted), but the lack of ability to adjust their FR is problematic. For someone who has a MiniDSP they would be great.
However, the 23Hz -3dB point for the sealed version makes it obvious that the amp has been EQ'ed to be as flat/deep as possible in an anechoic chamber. Putting them in a typical room is going to result in a boomy sound after room gain increases the low frequencies. Of course the ported sub would be the same but worse!
For anyone willing to do miniDSP/REW/measurement, I think, you would still be ahead of the game after spending the money for the miniDSP and mic to complement these!
If the sealed sub had less aggressive EQ, the $400 SB12-NSD would be a great buy!