I also flashed my GS308T without opening the case.
The commit instructions note that the OpenWrt ramdisk image can be flashed from the Netgear user interface. The Image0 slot should be used (selected from the Netgear user interface).
Do not flash the sysupgrade image from the Netgear user interface (if you do, you'll be opening the case and connecting a usb to serial dongle to try to de-brick it). You have to flash the initramfs image first, then scp the sysupgrade image to /tmp on your GS308T, then ssh into your GS308T and flash the sysupgrade image you scp'd to /tmp from the OpenWrt command line.
It used to be rather tricky to get to the device after flashing the initramfs image. Instructions and links in this thread also helped me out. The default configuration has since been changed in snapshot (and GS308T is not supported in 21.02) so that this should no longer be a source of confusion (unless you follow outdated guidance, which is why I've summarized the history).
As far as issues, the only issue I've encountered is that the LEDs on the ports do not light up or blink when you plug a cable in to the ports or data goes through them. This doesn't impact function though.
I can't help you on your last question.