P3D is essentially a FSX 10.something. It is derived from ESP, Microsoft's commercial offering, and currently something like SP3 or SP4 which MS never made. I don't have it but did try a free trial and it didn't make a huge difference to me on a pretty fast PC.
As it's essentially a fork of FSX 99% of FSX addons work in it, often it's only the license that forbids the use rather than a technical issue. Like the Lockheed license I guess each person decides how comfortable they are with the rules and how well they fit them.
I'm holding out to see what V2.0 brings. If you buy the current Academic license LM have stated there will be charge for the V2 upgrade. V2 should bring lots of useful enhancements including DX11 support. However there is no news of whether that will affect 3rd party addons. Not sure is 64 bit is planned either but it needs it IMHO.