I have used my TomTom for at least 7 years now. I get quarterly map updates.
The only time I have issues is when a new road has been made. I can clearly see that the new road is there and that is the way to go, so I ignore the routing.
Otherwise, my only minor complaint is that it doesn't always show the posted speed limits correctly. Usually it changes when the updated speed is posted. Instead it seems to not post anything, or shows 45 to be the limit. Of course the problem with that, is that the 45 might be correct when nearing a city.
As far as Garman is, my friend is on his fourth one, and he has thrown each one away because it shows incorrect info. If you want his old ones, just look along the side of the road and you can spot it.