MyTrafficX is, fortunately, not the only package out there that can produce AI in the sim.
Many of the aircraft in MyTraffic X are still FS9 models, so don't work properly in FSX, particularly not in DX10 mode, although the developer is working to change this and regularly releases updates - it's a very well supported product.
JustFlight's Traffic X is the only one I know right now that is 100% FSX native format.
Also, you can always convert free FS9 AI packs into FSX format for the most accurate, but most damaging to frame rate, AI experience.
I can't find a package called "Air Traffic X", though?
None of them will allow you to use AI specifically for formation flying, that's not how the FS AI engine works, but there are other tools to do that, although I don't use any of them. Others around here will probably be able to advise a lot more on that.
Personally, although I have MyTraffic X, I wasn't overly impressed by it and uninstalled it a long time ago. I used freeware FS9 models converted for a while but am now flying with the default AI until I decide whether or not to risk TrafficX instead.