I've been using this JD40 for some time now and wanted to give a quick experience report.
Basically, I love it. While at work I use a 60% board and while at home I use this JD40. The layout is sufficiently different that I've been able to develop the muscle memory for both board, and can now switch interchangeably between the two with almost no loss of accuracy or speed. (I'm obviously slower on the JD40 than on the 60%, but I mean that I don't need to relearn the layout every time I use it.)
I'm a huge fan of how close everything is to the home row. Even complex chords don't feel like a hassle because there's very little stretching that's necessary. I might have a leg up because I've been a heavy emacs user for some time, so I'm used to finger contortions of various sorts, but I expect that anyone so inclined could pick up this layout in a few days.
This is also the first board I've had that's fully programmable, and I'm finding it hard to go back. The teensy + hasu's firmware makes it super easy to tweak the layout as I figure out what works and what doesn't, what I rely on and what I don't. I've basically given my QFR up as a pass-around-the-office keyboard, but I expect that if I ever wanted to use it again I'd have to get a Frosty Flake for it
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riotonthebay loves 40%