FWIW, I got a TomTom 720 Traffic last December
The RDS isn't worth the extra; the signal is intermittent, although usually OK on major axes and in cities, but the information received isn't worth having. It's rarely up-to-date or complete.
Moreover the software's calculation of times if there is an obstruction on route is bizarre! EG: I left London for Leeds one evening. Tom Tom says 2 road works on route, journey time 9 hours! Go through the first road works with about 10 minute delay, remaining time changes to 6 hours; go through the second lot almost without slowing down about 50 miles from Leeds and the remaining time goes from 5 hours to 45 minutes. And there were several hold-ups not showing on the Tom Tom, some long-term. The trip actually took about 20 minutes longer than usual.
So I don't use the RDS traffic info any more. Radio 2 is better.Otherwise the unit is excellent, although prone to crashing and needing a reload of the software.