Don't know where you get your info from John, but I don't have to worry about paying for factory sat nav. software updates ??
There was an update available for my Mazda 3 while I owned that car and it was a free download/installation from the Mazda dealer. I didn't bother to get it anyway because as stated it worked brilliantly and was up to date enough when used in all my travels...
As far as the Merc goes from what I 've been told by my dealer, I'll be able to get software updates of all sorts not just the sat nav without expense...exactly what types of maps they are in the Merc I'm not sure of - if you really want to know I'll find out, all I can say is as before it works brilliantly with many different map and info display modes, more than enough info and modes for any trip anywhere
Again I don't think I'll have to bother even with that one, because in future I'll be most likely using my smart phone to direct stream sat nav apps to the carputer in the Merc. in fact I'll be direct streaming any other useful app I want or need
My Garmin 390T will sometimes drop its signal and take ages to reaquire it, my 3790T has also lost its signal a couple of times but is more solid than the 390T...
I suppose for vehicles without built in sat navs you have no choice but to get aftermarket, but for vehicles with built in units it's a total benefit in alot of aspects and you'll never want to bother with a separate unit again, it's so convenient you don't have to bother having it hanging somewhere with wires everywhere and the possibility of theft and damage to your car, unless you go to the effort of a neat concealed install as I've done with both my 390T and 3790T in 2 other cars of mine