I've been really impressed with my GO 520 Music Edition. It's intuitive interface, extensive list of features, and overall performance have won me over.
For the most part, the menu system is very clear and natural. I did, however, find that a couple of the options I wanted to turn off were tucked away in obscure places, but this is a minor niggle. The menu items you will need to access regularly are right where you'd expect to find them. Connecting it up to my Sony K800i phone was a breeze, and it all worked perfectly, first time, over Bluetooth.
The unit's performance has exceeded my expectations. The GPS locking is fast and strong (even deep inside my house), and the overall speed of calculations and the display is very impressive.
Audio quality through the built-in speaker is not, to my ears, as clear as my old GO 300, but it's still more than up to the task. You can route the instructions and/or music through your car stereo (via an FM frequency) if you'd prefer. I haven't yet connected my iPod Touch up to the unit, but I've read that I can actually control the iPod from the GO 520's touch screen.
As soon as I connected the GO 520 to my PC (Windows XP), the TomTom home application updated the software to the latest version, and downloaded the latest "safety" camera database. You get a latest map guarantee, that lasts for 30 days. The GO 520 sits in a desktop dock (supplied) and charges when connected to your computer.
I can't recommend this GO 520 Music Edition enough.