I agree, not necessarily, but SVS and "poorly designed" aren't things I would put together regardless. The Plus driver has quite a bit more capability than the NSD, however it is in a sealed enclosure and it isn't a simple matter to overcome that.
Looking at the charts, the SB-12 gives up about 2-3dB across the range and drops off significantly earlier than the NSD around 22Hz, so I'd probably opt for the NSD (and it is $100 less).