Recently installed OpenWRT on the NSA325v2 and wanted to mention that the u-boot installation process went slightly different than the docs indicated.
>> setenv ipaddr 192.168.1.101
>> setenv serverip 192.168.1.100
>> tftp u-boot.kwb
That last command was documented in https://openwrt.org/toh/zyxel/nsa325#installation1 but requires an address and failed. I was unable to use any USB key in the stock u-boot with or without a powered hub, only after updating did my USB key show up. So I had to work around this. The working process was:
>> setenv ipaddr 192.168.1.101
>> setenv serverip 192.168.1.100
>> tftp 0x1000000 u-boot.kwb
>> nand erase 0x0 0x100000
>> nand write 0x1000000 0x00000 0x100000
>> reset
Now I had a fully working u-boot and could proceed easily.
I found space to install a cheap USB-C FTDI adapter inside the shell of the product for easy access to the serial console.
IMO this addition really helps with the overall usability of the product and removes most concerns about failed upgrades etc.