Bill,
I haven't had my B long enough for a long term check of the computers accuracy; but, your fuel consumption is very reasonable for mainly urban driving.
I drove to Abbotsford airport today, 175 Km return, and the trip consumption was 8.4 liters
which was very good considering the trip was in a driving rain storm and we had four people and some luggage. I tend to believe the trip computer is probably very accurate because MB does not want litigation and a black eye ( think Mazda and HP claims.).