The Unicomp Space Savers are different from the old traditional Space Savers. I have a picture of them here.

The top is an 80s space saver, the middle a newish Unicomp Spacesaver, and the bottom an early 90s Model M.
The two older IBMs are, I dare say, built a little tougher than this particular model of Unicomp (though the Unicomp still feels a lot more solid than, for instance, the Logitechs I am stuck with at work, and the Cherry I am playing around with now). This may or may not be the case with with the Unicomp version of the traditional Model M however.
And the older IBM's I think may be a bit clickier, though it is a fairly subtle difference. Even if we posit the Unicomp is inferior to the original IBMs, it is still a huge improvement over the craptastic Logitechs I use at work.
As with Mikecase00, my sample is small.
