First lets talk about the design. The starting point for the shape, was a standard business card i.e. 8.9 x 5.1 cm. I looked at many e-paper displays. GDEW027W3 fitted well and was affordable. I had bought a HAT for Raspberry Pi with that exact display on it. Also it is available from my local electronic component supplier. All said that was actually not the perfect choice. I found a flexible display that is the same size, but thinner and has better resolution. Unfortunately it was too expensive and not readily available. 

I went for 1 mm thick PCB. I was afraid that 0.8 mm board would flex too much and break the the display. I have decided to round the edges of the board to protect people from getting hurt. Also the sharp corner can get stuck in your pocket, when trying to get the card out.

The nRF52833 DK, that I got  for developing software, had it's USB ports indented. I thought that was very clever and decide to do the same for both USB and flat flex. This way I eliminated  two snagging hazard. Also the connectors themselves are very low profile 1mm for the display and the USB is middle mounted. 

The LP103053 battery is just 1mm thick as well. The down side is its low capacity. I have chosen a low profile buttons for nav. The debugging port is the same as the port on the nRF52833. This made my life easier. I was not afraid of pulling wires, bad connections or clips popping off. Also the debug connectors are keyed and you can't connect the cable backwards. The down side is that it had to be removed after programming the final PCB. 

This is why the board has that shape.