I've been using the FlightXML2 API for a while now. Overall I really like it. There is one strange omission that is easily worked around by filtering the returned data but still seems like it should be supported.
If I know the faFlightID of a flight, I should be able to lookup a single flight by that ID. Right now if I want the information returned by FlightInfoEx for that flight, I have to make a call to FlightInfoEx with the ident for the flight, and then filter the list of results for the one with the matching faFlightID that I'm interested in.
Please add a new method to get equivalent information to FlightInfoEx but with a faFlightID as the input, or add a filter to FlightInfoEx that can be specified in the request itself. It seems like a looking up a single flight should also be billed at a lower rate to calling FlightInfoEx which can return many results.