The effort on creating or designing something need to be respected. I do respect all the designers.
In lieu of obtaining permission, you should minimally credit the original design.
If you don't have the decency to pay such simple courtesy, you are a COPYCAT.
actually, i messaged back and forth with duck about this today, he couldn't care less
the sides look nothing like the blackbird, which is all he cares about really
unless you'd like to get pissy about 96key layouts too, since duck came up with that as well, and how many of those credit him?
this is just how the community is, something becomes hard enough to get, a copy will eventually pop up
if he was selling these on taobao as "duck blackbird" i'd be annoyed, sure, but this is a unique design, so that's not a concern