Yesterday, I unboxed my NIB IBM Model M Space Saving Keyboard (SSK), birthdate 13 September 1990. See below for a closeup view of the PBT dye-sub keycaps, showing the extra legends for the embedded numeric keypad and navigation keys.
Although I rarely use the embedded numeric keypad or embedded navigation keys, this is a nice touch that is not found on many TKL boards (the RF 87u is the only other board of which I am aware that has this feature -- please let me know if there are others).
Before acquiring the SSK, I used a full-size IBM Model M. For various reasons, I decided that I would like to move the mouse closer to the midline. This prompted a search for keyboards in the 60% - TKL (80%) range. I tried a number of boards, including the following: Ducky TKL with Cherry browns, Filco MJ2 TKL Ninja with Cherry blues, and the Leopold FC660M with Cherry blues.
Build quality of the Ducky was disappointing -- the case was not true and wobbled on the desk, and the extensible feet lacked a rubberized coating, so that the keyboard had a tendency to slide. Typing action and keycap feel were reasonably good, but I did not like the appearance of the keycaps when the red LEDs were not activated.
The Filco case was solid and true with no wobble, and the rubberized feet kept the board planted firmly on the desk. Typing action was crisp but too light for my taste, and my speed and accuracy suffered. The ninja keycaps were not for me, both with respect to legiibity and feel, so I replaced them with the classic beige "Olivetti" set from Originative. The new keycaps improved the appearance and legibility of the board, but the feel of double-shot ABS was still not as good as PBT.
Leopold has a winner in the FC660M. The compact design is elegant and efficient. It has a mostly standard layout in the main typing area, along with a minimal and highly intuitive Fn layer. The keycaps are PBT, but they are too dark for good legibility, so I replaced them using a combination of white and gray dye-sub PBT sets from Originative. Build quality is outstanding. The board is solid and true, and it remains rooted to wherever it is placed on the desk. Nevertheless, my typing speed and accuracy on the Leopold were not as good as on the original Model M or the SSK.
The IBM SSK is a masterpiece. It has all the features I want in a keyboard. The dye-sub PBT keycaps look and feel wonderful, so that despite my membership in GH, I do not feel compelled to replace any of them. The buckling spring switches provide just the right resistance and aural/tactile feedback for the best typing experience and performance as far as I am concerned. Typing on the SSK is sure and precise, giving me a feeling of confidence in my typing that I do not feel with other keyboards. While not nearly as small as the FC660M or the Filco TKL, the IBM SSK is substantially smaller than the full-size Model M, yet its considerable mass and exceptional build quality keep it sitting squarely on the desk. Finally, not that anyone looking for a buckling spring keyboard would be concerned about noise, I find that the SSK is quieter than my full-size Model M.
Overall, I prefer the IBM Model M SSK over any other keyboard I have ever used. In comparison with recent acquisitions, I would rate the Leopold FC660M second to the SSK, but my complete typing experience including speed and accuracy is far better on the IBM SSK.