I added a clip on the bottom case to allow the case to be attached to aluminum profiles (30x30).
First time it's hard to remove, but don't panic, squeeze the clip and incline the case laterally.
Update:
Added a new top part variant (OPIZERO-TOP-USB.stl) which allows you to add another USB port via female breakout board. This can be handy for those who are having misery with on-board Wi-Fi, So that they can add a cheap $2 dongle such as Ralink mt7601u.
The author remixed this model.