When we say GSX replaces ParkMe, it means instead of having a separate key for ParkMe, it will all integrated in the GSX menu, which is more logical, and it also save a keypress. But GSX includes all the previous functions of ParkMe, adding the Marshaller, and it's free with FSDT airports, so it will only improve upon ParkMe.
Of course, being universal, with GSX you'll have ParkMe function at every parking of every FSX airport (with Marshallers, unless we do a specific airport customization file, adding Docking system if present), while with the current ParkMe, it only works at FSDT airports, and only with Docking Systems.