Print on flattest side. The clearance should be forgiving enough for the buttons with lower quality prints. I used M3 bolts to screw directly into the screw holes but a nut can be added if desired.
The author remixed this model.
Cut out some area around the reset and boot buttons to make them easier to press through the lid and trimmed the pin edge of the board to make it flush with the PCB and have better clearance with the official rubber case on the flipper zero itself.