The main draw of PilotEdge is not being able to see other aircraft in the pattern, it's the fact that ATC is provided within the coverage areas 15 hours a day, 7 days a week. As you can imagine, that costs quite a bit of money to operate as the controllers are paid to be there. Every multiplayer system lets you see other airplanes (that's the definition of multiplayer), but there aren't any other systems that provide ATC on a regular schedule.
Regarding the quality of other pilots, the pay wall and age limit (18+ unless you've soloed in the real world) tends to keep away any malicious actors or trolls. If not, every controller has the power to ban and disconnect users.
As for being expensive, it's all relative, but it's actually $14.92/mth if you use the annual subscription. That lets you choose between ZLA or the Western US coverage area. If you conduct a 2hr flight (or set of flights), once each week, it's < $2/hr.
Regarding support with FS2, as someone mentioned above, there needs to be an API which permits traffic injection and animation. On top of that, they need animated 3d models (which is a fairly large undertaking). Other than that, integration is simple and could be done with a few hundred lines of code as we have a utility which allows for easy integration with just about any sim. The utility handles 90% of the heavy lifting in terms of interaction with the PE server. We used it to build an implementation for DCS, it worked well.