I have 3 QuietKeys at home and the office. Two of them are very comfortable to use and are built well (the keys move on square sliders, they have a metal plate backing, and they have two no-mark, no-slip, rubber tread strips under their front edges) and the third feels awful.
The two good ones I have are both by Silitek (which I learned right here on geekhack :-D). The third is from a different manufacturer, whose name I forget, that made a quietkey that is quiet, but also stiff, spungy, and overall not very comfortable.
Just out of curiosity, what models are yours MS?