I've recently acquired a JJ40 (Ortholinear 4x12) that I'm trying to bend my mind (and my fingers) around.
Since I have had a couple of issues straight from the start, I gave it some time and forced myself to type exclusively on that board for a while.
I used my normal full size keyboard for gaming only - mainly because I was too lazy to remap all the game buttons.
When I was ready to give up, I saw a video about someone who explained the concept. He said something nice. He said 'Instead of moving your hands to the keys, you move the keys to your hands' - he meant the multiple layers and the concept of having access to every key with your hands in the home position. That somehow stuck with me. I tweaked my setup some more and right now, I get along more or less splendidly, only occasionally running into the need of typing somthing unusular like ~ or ^ and not remembering where (or if) that key is mapped.
The ortho layout does a couple of things to you. First of all, it annoys you big time when for the 100th time you type an x instead of a z. But all those bottom row keys really come in handy. I mapped space to the two in the middle and have FN1 and FN2 flanking those, but thanks to the power of qmk, those also act as space when tapped. Same goes for enter, which is right shift for press&hold and enter on tap. I just mapped things to where my hands thought they are and suddenly, my speed increased. You can't get rid of the habit of using a 100% layout for three decades in just a few days, but that's not the point I'm (slowly) getting to.
That point is: I kinda fell in love with that tiny layout. So I started looking at other 40% layouts. The JD40 among them. And I realized that they do not have enough keys for my taste. Your standard ortholinear board of that size has 47 or 48 keys (depending on whether or not you have that 2u space bar). The JD40 has only 44. At this level of minimalism, every single key counts. Three more keys mean three more possible layers.
I frequently type in German and occasionally in French, so I need äöüßéèê and such. Without those, I might get away with three layer keys, but I simply mapped all those characters to a fourth layer.
The straight layout is a bit weird to get into your muscle memory, but the fact that every single key is 1U and every single key is in a fixed grid makes navigation totally possible and a lot easier than thought.
I like what you did to that layout. I can't see the benefit of having that right shift key not sitting on the end of it's row, this would be just weird to type on. But having dipped my toes into 40% waters, I'd always choose to sacrifice staggered keys for straight rows of 1U keys.
