I've used this app since it came out a few years ago. There are several other apps out there that do similar things but have stuck with FlightTrack because it just works. You get push notifications as soon as there's a delay or any changes to your flight. Most of the time, the changes in flight departures/arrivals is updated before the TV's in the airport, which give you an advantage when you need to rebook due to a cancelled or delayed flight(shorter lines, because people at the gate learn about it after you). It's also incredibly useful when you're planning your trip to the airport.
UPDATE: Although this app is available for both iPad and iPhone they currently don't sync, which is a huge annoyance. The funny thing is that they did use to sycn before the iOS 7 redesign. Hopefully they'll be adding that soon.
Saasler