I've tried the KB-1421 variant and it's decent. Decent tactile feedback, decent stabilization for extended keys(for once on a Dell KB), and I like the font, since it's not the usual generic Helvetica-like monolinear font with the $ sign that's not quite Helvetica. Blue LEDs are a nice touch. Overall, I think they're really nice looking keyboards. They nail the no bezel look (unlike the older "rattraps") by maintaining clean lines and keeping protrusions to a minimum, something the older "rattraps" failed at miserably.
I can also confirm that the keycaps are flatter, and rather shallow, though throw is decent. Tactile feedback is great for a domer. If I'd ever pay $22 for a rubber dome, I'd probably get one of them. I can't comment on the Sk-8175 variant though. Also, I haven't touched one in about 4 months, but I think they weighed decent and probably have a metal backplate (not sure however)
They come packaged with the newer Dell Optiplexes with the new styling (with gunmetalish mesh design), not the old ones with light silver tops/sides and black fronts.
And the old ones ("rattraps"), I will say, sucked, though I don't hate my SK-8115 that much. Keys felt cheap, the legends were thin and cheap, the whole thing looked cheap in general, the thing was featherweight and lacked a metal backplate (can you say cheap?), it had almost no stabilization except on spacebar and right shift, the deeper keys on the front row were very wobbly, and it was just plain ugly with all the protrusions and what not. I did like the wider(or deeper?) spacebar a bit though.