I have the Nav Pro to. Is it worth the money, of course not, didn't stop me specifying it though

It's a decent unit and the larger screen really finishes off the dash in my opinion, and it shows the detailed maps off to their best.
As to the SSD, it's mainly there for storing the maps which are huge (about 20gb), and contains 3d representations of major buildings in the big cities. Voice control (standard on the Nav Pro) is fairly well implemented as well. The remainder of the SSD space is available for music files, although to be honest, with 2 SD cards slots (both available at the same time for music files as the maps don't forget are on the SSD), DVD slot and an Ipod / USB connection, I really don't see me ever using the storage on the SSD for music.
Also, the NAV Pro has Gracenotes implementation which means if you insert a CD into the DVD slot, there is a very good chance that it's stored in the Gracenotes database and so rather than seeing "Track 1" "Track 2" etc, you actually get full artist and tracks names as well as cover art displaying on the screen. I've only so far had one CD which wasn't recognised.
I've added speed cameras as personal POI's to mine (which I don't think you can do on the smaller units ?), and whilst it doesn't give an audio "bong" when near, does provide a very clear visual representation of the cameras on a route.
All in all a decent unit, but it is certainly a bit too dear.