I've had the TomTom Go 520T for about a month now and I've been very impressed by it. Works very well and has managed to shave impressive amounts of time off journeys I take regularly.
The 520 can be upgraded when you connect it to TomTom Home (the software is included) to the latest onboard software as well as the latest maps. This gives it all the features of the later version TomTom 530, but for £100 less! The added features include advanced lane management, which creates a nice 3D graphical picture of motorway junctions as you approach them and shows you clearly which lane to be in, which is very handy. Another feature is IQ Routes which determines the most efficient route for you to take depending on the time of day and day of the year, based on other TomTom user's experiences. This can mean on a return journey you end up travelling home a different way to the way you travelled out, but it can save a lot of time.
Instructions are very clear, although I found the computerised voices occasionally garbled words at high volumes, this may be an intermittant thing.
My mobile phone (Samsung F490) was not listed as compatible but works well with the Bluetooth hands free function, although I cannot send or receive texts, but that is a small niggle.
I found the RDS Traffic receiver worked well - and locked onto the station quickly. Although items listed as 'Traffic' can be minor inconveniences such as narrow lanes so should be taken with a pinch of salt.
Maps are good - although I have found a few roundabouts which aren't displayed on the map, a bit of common sense needs to be used!
There are many more benefits to this device - I won't go into them all, just recommend you buy the TomTom 520T and find out for yourself! All in all I'm very satisfied with my purchase.