Searching for new device

[frollic]

Quality of the VDSL modem

I think you're making this more difficult than it needs to be. NBN FTTN only supports 17a with vectoring. Anything greater will be unused/wasted. Updates are likely irrelevant as I doubt anybody is working on technology as old as what NBN use anyway (Europe has 35b, super-vectoring, g-fast, etc). I suggest you take the advice given already. Get an xrx200 based device and flash OpenWrt OR anything that supports 17a+vectoring and allows you to configure it as a full bridge (many don't). Use that…