I tried to install latest Openwrt firmware (OpenWrt 18.06.5) to my Newly acquired Ubiquiti Edgerouter X and below is the result.
ubnt@ubnt:~$ add system image /tmp/openwrt-18.06.5-ramips-mt7621-ubnt-erx-initramfs-kernel.bin
Checking upgrade image...Upgrade image does not support the device. Upgrade failed.
/home/ubnt
ubnt@ubnt:~$
OSedge Version:
ubnt@ubnt:~$ show system image
The system currently has the following image(s) installed: