RCD have been invented to check for earth leakages.
A false connection to the neutral is a partial or total short circuit. It can be detected by overcurrent protecting devices or more sophisticated current/power observing electronic devices. But never by an RCD.
Whether with or without neutral, an RCD will work as well, except for the test button. The way of connecting with correct test button function to such systems is often written on the device itself.
Price: So what is it down under?? In Germany we start with 25 € as said above.
