OK, this is definitely not best practice, but I just dirty upgrade, no dismount USBs (I have 2 attached) nor disconnect. It usually just works. So, I wouldn't worry about it. Been doing this on RT-AC68U and later RT-AC86U). Also, every now and then (say every 10 dirtys), I'll do a rebuild from scratch. Also, like many here, I load alphas and betas when available, not just release.Something I'm not clear on a dirty flash: Is it better to reboot, then dismount the usb drive and flash firmware, or dismount, reboot, then flash?
I also save a copy of the settings and JFFS partition before each flash, so I can always go back if something goes wrong.
Probably should unmount, though.