Just FYI, I believe that Horizon advertises 100% compatibility between the two. If I were buying a new one, I'd buy the Pro.
I have the standard system for my M11, but my B4 is running the 'Pro' micro receiver without any issues. You just get only 1/2 of the unnoticeable improvement in response speed
I do remember reading something about the antenna being sturdier in the Pro system for the M11 as well - but if you 'mod' it into the factory hole on the Tx this doesn't matter.