I have a couple of TEK 209, a standard legend one at work, a black one at home, with a few white keys spelling out my initials for maximum geekiness...
I like them for both coding and writing. I'm not going to go over the stuff that others mentioned: it's all true, it's small and sturdy, the company sucks to deal with, etc. So, here's some random observations:
I've adapted to the shift keys, but am still struggling with slash, tab, and apostrophe.
I have no problems with them on my MacBook Pro, but I have never plugged one directly into the MacBook USB. That may be what saves me. One connects to an IOGear KVM which connects to a Thinkpad and to the built-in USB hub of a Dell monitor connected to the MacBook. The other goes to a Dell monitor which gets plugged into either a MacBook or a PC.
Speaking of the KVM, it works great with an IOGear KVM. Before you use it, you must plug in a conventional keyboard and do the alternate switch key thing. Once you do that, the IOGear stays set for life, and a double tap of the left control key of the TEK toggles boards.
The keycaps wear quicker than just about anything else I've ever used, especially the non-standard split space-bars and the backspace. I don't know who they had mold the dang things. To add insult to injury, the white legends on the high use keys get grungy. Which makes the N, S, I, E, etc. especially ugly.
It is profile compatible with WASD keys, except for the five weird shaped keys in the center and the split spacebars.
The keycaps look black, but they're actually translucent smoked grey. Not just the three that light up, all of them, except possibly the center 5. I have no idea if this can be exploited in any meaningful way.
Both of mine are set to PC mode, because Mac mode seems to cause more problems than it cures. The MacBook is set to make the left and right control keys "command" keys and the "super" key a control. The dead keys in the corners can't be remapped with software when it's in PC mode.
I frequently end up with my right hand one column left of home, and I have no idea why.
The pinky columns are not shifted down enough.
The enter key results in the occasional "accidental send".