Wtih 14yrs in the airline industry Ive tried most of the flight tracking apps out there, and this one consistently proves itself to be the best. I especially like how the flights are separated into "trips" and as you open a trip its only the flights within that trip that get updated. Saves bandwidth, saves time. Calendar mirroring is another excellent feature - enter the flights once in this app, choose which calendar to sync with, and they all appear in it.
The developer is super responsive. Any time Ive had a question hes always been ready and willing to help, although the app is so well written Ive not had to ask much!
I had an interesting issue with synchronization between my iPhone and iPad. Because I was running different OSs on each the iCloud backups werent talking to each other. This was an Apple thing - iOS8 upgraded iCloud Drive and my iPhone was still on iOS7. However the app also syncs with TripIt (you dont need the pro version to do this) so now my two devices stay in sync perfectly.
This app comes highly recommended.