VERSION 1.1:
v1.1 is more difficult to insert, but fits the device better. I printed this in Inland's high-speed PLA+ in periwinkle blue, so I've updated the print settings section to reflect those options as well.

v1.1 changes:

• Redesigned bottom opening to reduce cracking when inserting.
• Increased height to account for screen protectors (14mm->15mm).
• Decreased width of carrying strap cutout (9mm->8mm).
• Decreased widths of microphone(?) cutouts at the top (10mm->9mm).
• Raised cutouts for power button, media buttons, and function slider by 0.5mm.
• Added lip to top of frame to hide the panel gap.

ORIGINAL V1:
I bought the M300 case that HiBy sells, but I was very disappointed: the power button was constantly pressed down and when you press one of the joint buttons, both were pressed. I tried cutting out parts of the TPU, but it made pressing the buttons extremely difficult.

I decided to try my hand at modeling a case for the M300 and I think it turned out pretty well given my lack of experience in 3D modeling anything more complex than a rectangle.

Each port and button is given ample room. The case has <1mm of give, but it stays on snugly.

If you have any suggestions on how I can improve this design, please let me know in the comments!