After putting over 1000 miles on mine, it is a more accurate realtime mpg. I use a solid half city, half highway mile driving history and get almost 40mpg combined. Highway gets better than listed and city less than listed. So as usual, these metrics are a guide not reality.
I noticed my mpg wasn't the greatest the first few hundred miles. It gets much better after that. Just a guess as I am not an expert, but the battery may need breaking-in before the computer decides to use the electric mode more. Just my 2 cents.