You can find a discussion here:
https://www.volvoforums.org.uk/showthread.php?t=284843
For what it is worth , my opinion was:
I got mine done before Christmas.
The inbuilt TMC which updates via FM radio is quite hit and miss when it comes to getting good, regular reception. The TMC symbol on screen only appears to be on screen about 50% of the time.
The RTTI software allows you to receive traffic updates via a linked mobile phone or, I presume, an inbuilt modem, so it is available and providing data practically continuously, just like on my standalone Tomtom in the old BMW.
Shortcomings - I would like an on-screen icon to show that I am still connected to the traffic update website because it can be difficult to trust it when headed into a notorious bottleneck without even amber warning on the track ahead. It has happened once or twice when, as expected, there is heavy traffic but turns out the phone had disconnected itself.
Mine cost just under 30 euro when done alongside towing module software (76 euro inc vat, total for both). I was happy to pay 30 euro for it to give it a go but not sure I would spend £50 for the amount of time I need it. I definitely wouldn't pay £80 for it.
The actual RTTI software costs less than 20 euro retail price so worth negotiating doing it alongside any other work at a dealer.