linw: I see the Fritzbox has an ADSL/VDSL modem front end so does this get disabled for a UFB connection?
as richms said devices like these can function as a DSL OR Ethernet router at a time.
You can only use it as one of these at a time, However I do not believe Snap would limit the DSL functionality of the device via any other means, So VDSL functionality of the device would still be there if you chose to move to VDSL instead.