I have one of these. The keycaps are definitely nice. The numpad keys and enter key have a definite shine from wear, but the rest of the keys are in good shape. YMMV, of course.
At $2 to $3 a pop I'd recommend instead getting one of these. (http://geekhack.org/showthread.php?t=8652)
You get a lot of relegendables. And maybe a keyboard you like although most POS keyboards are too worn for my taste. The Relegendables don't get as much use as the main cluster though.
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These.
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Oooohhhh! I would love to get some of these for my model M too. I know I've seen them for the M, but like mentioned, they can be expensive. Personally, I would love to get a complete set for all of the single space keys.