I have installed with many difficulty with SSH a OpenWRT firmware ( 2 box's )
I also bought two just because the case had a port usb3
I have connected a HDD USB3 / uas and SSD and i have a poor USB3 speed ( not in WIFI mode but with LAN port )
I even have USB3 boxes that do not work at all
If i compare with a WR1200JS with USB2 i have the same speed
it costs less
it also has many diodes to visualize its operation
Also easy for install OpenWRT
finally I think there is absolutely no interest to buy the XIAOMI product