Well, my Becker is not so great. Sent me to the wrong roads many times. Classic one is asking me to leave motorway and join again. It's easy to ignore when I know the road and know it's doing this, but a little bit annoying when abroad and driving first time on particular route. Last time in France it asked me to go left and I could see the route is going to the right.
Heathrow, leaving towards Maidenhead, it says turn right and lanes are also showing turn right but to go to Maidenhead, you have to turn left and that's what overhead signs on the road say.
So I can't trust it and have to check road signs to make sure I'm turning to the direction I want to go.
But I think it's better than Comand Online in terms of setting options, stopovers, showing how far is to next turn/junction, showing arrival time and distance on top left hand side corner when I can see it.
If I buy a car without navigation already included in price I will go and buy new Garmin or TomTom. I'm not going to trust another built in navigation again.