It can't be compared with FSX since those two simulators have totally different philosophy.
Despite it's advantages XPL has it's downsides. It uses openGL instead of DIRECT X and thats why it looks different in graphical terms. XPL uses 3d model of the aircraft to calculate aerodynamics. It can be very tricky though.
There are a lot more systems that are simulated by default code that FSX lacks. Those variables can be easily manipulated for 3rd party addons.
XPL is newer simulator and that's why it has less addons than FSX. But I love it anyway.
There are a variety of aircraft for XPL that are not simulated for FSX...
Try it anyway. It will give you different simulation feel than FSX.