Now, in the end, I decided to replace it with mt6000, and I have two ERX in hand (I replaced the other ERX with mt6000 last year). I don't need two backups, so I decided to sell one of them. Can I flash the stock firmware, even after I changed the partition layout? Or would it be actually better, if I sell it with openwrt already on it?
I would flash the latest version then do firstboot && reboot. This will wipe your settings. Check to make sure that worked and sell it with “running latest OpenWrt version”.
It speeds up basic networking. Like, a lot. The downside is, it may conflict with SQM, but since you don't have SQM installed and configured, this is not important.
Come to think of it, I recently upgraded a USG unit to 25.12 and ran a unidirectional iperf3 test LAN-to-WAN (iperf3 server sitting on the WAN port, iperf3 client, on a LAN port). Without offloading, I got 140 Mbps; with offloading, 930 Mbps (which is basically Gigabit minus "housekeeping" traffic). Bidirectional tests showed combined throughput of 190 Mbps without offloading and 1,010 Mbps with offloading.
