Looks interesting but reading the known issues it seems you can't flash back to an earlier version.
You have to ask for special version of the older firmware.
Not good as this should be available for general download in case you need to go back due to buggy software. So before I flash I'm going to ask tech support for the get me out of jail version....

You can check to see if this might affect your model by checking the output of "status system" in the router's CLI and if the hardware version has no suffix, it will be safe to upgrade or downgrade the firmware without any issues
I do recommend backing up the router's configuration before updating regardless