Interesting. I take it from the description that the FTSC-type switch is similar to the old buckling-spring switches used in early keyboards?
I think it's more like the keyboard pictured in my avatar. Here's a
Picture from google image search.
Basically the keycaps are just the tops and the stems, that normal keycaps have to reach the domes, stay in the board. Apart from that I don't think it's any different from a normal rubber dome keyboard though. Although this is just a guess so if someone knows better go ahead and correct me.
Whether the model M is mechanical depends on how you're classifying. As it shares many characteristics ('clickiness', feel, longevity, spring use) with the alpls/cherries/strongman switches you could call it mechanical, it's easiest just to call it buckling spring and leave it at that though.