@Ken-Clarkson I use a Zumo 390 and can export routes created in MRA to it with no problem whatsoever, including the route accurately following roads and with all waypoints intact, and have put them to use with complete success. In the Connector, be sure to select .gpx 1.0 as the file type, not .gpx 1.1. In my experience, using 1.1 files will result in those straight lines on the 390 - I think these are best left to the Zumo XT and, possibly (though I'm not certain) the 396 and 595 models.
I hope this helps. Please let us know how you get on