I never had the pleasure of playing on a real Model-D (original or reissue) but I have a Moog Sub 37 and the difference in build quality between that and the Poly D is very noticeable.
That said, the Poly D sounds *amazing* and I think Behringer have quite cleverly introduced additional features re: poly, CV, etc.
Some people seem to think this is overpriced, but for a very good (sound-wise) clone of an icon, and with additional features to boot, I think it's worth the money.
Just don't expect it to be as well built as a real Moog. It feels a bit cheap, although I wouldn't necessarily say flimsy. Just ... cheap.