Eagle Dynamics created a simulation engine that, in principal, can simulate anything from fast jets to bicycles. P-51D was something to show off what their sim engine was capable of... a tech demo of sorts. Progress was quick... 1 + 1 = 2 and so they decided to market it as a commercial add-on.
Think outside the box for a moment. This P-51 can drop bombs, fire bullets and missiles. You can go online and have a dogfight with another P-51 user. I'm sure there will be an online ladder-challenges as soon as this thing goes gold. If this module succeeds it only stands to reason that more WWII planes will follow... possibly period terrain as well. And yes... 3rd parties are lining up to take up this challenge as this too is part of ED's business model. I'm not going to start comparing this P-51 with any of the others available for FSX. To be honest, I haven't tried any of them. What I do know is that ED is commited to simulate everything in minute detail. Their flight-model engine is fantastic and I've never seen anything quite like it...
regards
PS: none of this flying around in some part of the world admiring the scenery bull.... If that rocks your boat then by all means... but this is a combat aircraft. You think you're the Ace of the Base? Well, then try and see if you can actually operate this piece of machinery to it's limits against other "Aces"... You'll be surprised, I'm sure. :-)