They just pushed Orb 1.0.7 that makes the autoupdate package optional for now, so installs work on the Slate AX (And I suspect other Gl.iNet devices too).
I was able to just run the default command from the orb docs for the install to work now. If you select Yes for AutoUpdate, then that part of the install will fail, but the main part still works. So after installing it, use the link provided in the output to link your Router to your Orb account, or open your Orb app and it will find it on the network and you can add it.
