Although I have never owned nor used a Unicomp Model M, I agree with fohat.digs on the reliability. If he is wearing out rubber domes through use, and since he "kind of attacks the board," I would recommend a Model M for him without hesitation. With normal use, even vintage IBM and Lexmark Model M's will long outlive their owners. Or take us to the point where the keyboard is no longer a ubiquitous input device, but rather an archaic one.
I also heartily recommend Filco for MX-based full size keyboards. You cannot go wrong with a Filco. I have several TKL Filcos, and they are probably the highest quality production keyboards I have used. I haven't used the Ducky boards, but from the reviews, they seem like a quality product. You could also consider the WASD keyboard. Weyman and the crew at WASD have some of the best customer service in the business. And lastly, there is now Keycool with their 108-key boards. MechanicalKeyboards has them in-stock,
here. I am typing this on a Keycool 87, and I am very impressed by the Keycool brand. See my review,
here.