Yes the RDS traffic is fine for many users, hower it differs from the SIM traffic. RDS uses the signal broadcast from the radio stations which is fine in many cases, but sometimes you can be in a jam as the broadcast can be slow being sent. So you might find that a jab is cleared alrady but the signal does not say it in real time.

One the other hand, the live traffice is obtained from TomTom via the Vodafone networks so can adjust live when mobile SIMs move from cell to cell and location from transmitters and receivers know this....e.g. your smartphone has location built into it- yes?
So tomtom is able to send this info to the units or smartphone live or within minutes, so it is better. Also you will note on many motorways and major roads, the sensors on the bridges also send information to units. My old Vectra had traffic info provided for a licence fee. Handy but not perfect