Install Edgerouter ER4 Successful experience

I have a spare Edgerouter ER4. Try to install the Openwrt onto it.
Since it is through serial connection, I need to buy the suitable cable. The PL2303 did not work, I need to use the FTDI232 chips one. Of course it is more expensive but works with Edgerouter well.
Basically I follow the instruction and command from the official commit here.
The link is :;a=commit;h=dd651e54cc5eadba480a56a7d2c18471e560f491

However, the mounting of flash drive does not work for me. So after flashing the kernel, I need to use wget to download the Sysupgrade file. Since this is not my main router. I need to uci another lan address and make internet connection.

The steps are quite complicated. Missing one step will take me to the first step again. It involves recover the edge router the factory firmware. Once I flash the kernel and the firmware Sysupgrade is not on the same day. So, installing openvpn cause kernel incompatible issue. I need to reinstall the whole process again to make it work. So far, I use Adblock, Openvpn quite smoothly. The sad thing is the hardware offload is not supported for this router. The software offload still works for me and the speed is up to my expectation around 940 Mb/ 1G plan. Happy to share my experience here.