Just received a set of Corsair black double shot keycaps from Amazon. I haven't installed them yet but overall quality seems good. Mine don't have the smudges that an earlier poster said his have, but, like his, my "PGD" key has a small misalignment in the letters, the "G" is a tiny bit lower. But honestly, if I wasn't looking for the "PGD" error I probably wouldn't have noticed, it's very small.
I'm just glad that Corsair went to the trouble of offering these to its customers. I was going to buy a backup set of standard keys from Corsair for my K70 anyway, so to me the extra $20 was worth it. I've been in the IT field since the early 1980's and I have to admit that I love these corsair keyboards and plan on using no others so these double shots were a no-brainer. Ability to use on most Corsair keyboards plus most keyboards with cherry MX switches, {warning, some keyboards have a different size bottom row than Corsair keyboards}, is a big plus.
Will update when I get around to installing them.