Have been using this app for last 2 years. The max speed recording for ICF train is 121kmph while LHB is 156kmph when max speed of the same line is 110kmph and 130kmph respectively. Last month had a GPS report of bus journey had measured 20km less.
Every app has an error as it's measured with mobile signals. Whereismytrain also uses the same and some times shows error. We can consider the data as approx for general reference.