Hope you don't mind me reviving this thread. I'm in late-game X-Com Files and just got the AIRCAR. What's it good for?
I'm still using Rovers for undercover missions, which can hold 1 more agent. For regular missions I've got Skymarshall (cheap fuel), IronFist and (soon) Avenger.
I really haven't found any use for it anywhere. Like with many other XCF stuff it's just there for the kicks of it, not for any distinguishing use or purpose as far as one can see. By the point you get it, you have much better options on all fronts.
If it had the same special mission capability like the land rover, then I guess it might have some use as an undercover replacement. But it has no special mission capabilities (I dunno if this is an oversight, though it might be argued that a flying car could not go unnoticed).