1/ The N.S.A are not rarer than the Polaris: 1500 N.S.A versus 768 Polaris 68 Re Edition, 65 SS Boutique Editon, and 165 In platinum.
2/ I don't think the N.S.A IS an updated Memovox Compressor, you can hardly compare them, as they are very different in size, thickness, style, number of crowns, external bezel / internal for the MC Memo, different layout of the dial, etc...
3/ The Polaris and the N.S.A play on different grounds.
The Polaris is a Vintage, with modern solutions, and a faithful look to the original.
The N.S.A is closer to the Deep Sea Alarm than to the Polaris, because of its external bezel, and because of its 2 crowns instead of 3.
I am convinced that the N.S.A has already its fans, or will find them easily.
To me, it deserves more than to only be an erzats of the Polaris.
Best,
Nicolas