Or circa £200 if you sell your old one at a good price on eBay :D

Exactly +++

No brainier really!

Off topic, but it would be really useful if someone could produce a guide for the section sticky on which leads are required / compatible for which A8/S8 Versions and models, so that anyone needing to know which is the correct lead can look for the right type(s) +++

At present there are only a few cars the old Hex-usb+can doesn't fully support, and Paulrstaylor's Q7 is one of them. Also there was the odd task it couldn't do with UDS protocol modules, but still a very capable and useful tool.

D2/D3 All modules are KWP so the old Hex-usb+can is fine.
D4 is a mixture of KWP and UDS. Hex-usb+can works fine but it can't do an optical loop test where as the current Hex-net and Hex-V2 can. That may be the only task the old cable can't do on this car, so not enough to warrant an upgrade if you're an existing old cable owner.
D5 I'm going to guess is fully UDS and will probably need a current Hex-net or Hex-V2.

Overall Hex-net and Hex-V2 will support the future cars coming from the VW group and scans cars almost twice as fast as the old cable.

And just to add that the old VAGCOM can do everything with a D2, though not a D3 (just the engine IIRC).

(I still have a registered copy of VAGCOM/ VCDS-Lite and it has significant value for a trade-in at Ross-Tech, just can't decide what to use it for as I have a Hex-USB-CAN cable as well! Make me an offer?)