I did a bit of research, the DSE XH9949 is in fact a rebadged TP-Link TD-8840. I just stuck the latest (Australian) firmware for that unit onto my one and it works fine. No real benefit to it other than the colour scheme of the browser interface is a bit nicer. Plus it does DNS reservation and MAC cloning now :)

Presumably flashing back to the DSE firmware will work fine, I see no need to try it as the firmare is 2 years older than that from TP-Link.