This will work with connecting to the serial port. Assuming you have installed headers.
FTDT USB to TTL Serial Cable
As for the image. It is just a standard Rockchip firmware wrapped in a LUKS cocoon. Can it be flashed to another RK3328? Yes. Will it work? Not entirely. OS. Sure. but the stuff in /emulator reads from /proc/device-tree/model looking for HAXXXX. So when it does not see this it fails.
Ok then you should wait a few months until it goes final.... For the Edgerouter X it would be good to get a usb to serial ttl cable in case it bricks or another other router that has pins to hook on.
Something like this which I have.
https://www.amazon.com/gp/product/B07RBKCW3S/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
it's good to have for the edgerouter X and for other routers that have pins solder on...
Good to have in case you have a bad flash.