I have two Unicomps. One is a full-size Classic in Ivory, totally old-school, and the other is the smaller UltraClassic in black.
My impression of the quality is that they don't watch the cosmetic details as closely as IBM or Lexmark did. I knew this going in because I'm not the only one on the internet to say so. But you have to be ready to put up with plastic flash around the edges of the keys, molding swirls in the plastic (more visible on the black, apparently) and occasional other rough-around-the-edges stuff. I'm typing on the black one now, and I can see a little lump in the case's "body line" right above the F12 key, and some sloppy moldmaking in the punchout area where the mouse buttons would be if this was a trackpoint version. The keys all have visible flash down around the bottom edges, the works are a little bit to the right of where they should be to be aligned with the cutouts in the case, and the logo is 1990s hideous.
And I don't care about any of that. What matters is how it feels and performs, and it shines in that area. Every key is fast, perfectly tactile, and consistent. It doesn't have the finish of a real Model M, but it works and sounds and feels just like one. I can't speak to its longevity, because I haven't had it long enough to see how it holds up. But it feels right.
Bottom line is, if you want something that looks slick and polished to show your friends, get a Das or something. The Unicomp is not very impressive to look at. But if you want something satisfyingly clicky and clacky and don't care if it's kind of a butterface, you could do worse for $80.