There are many apps or websites that can create or save to the gpx file format. The gps should be able to read and interpret the file. However there might be discrepancies in the results if the app that created the gpx file uses a different map base than the one loaded in the gps. This is why I prefer to use basecamp to load the files.
I have found whenever I receive a route it's best to open in basecamp recalculate make sure (the route can change) its what you want then load to NAV. I agree the way it was created makes a difference including the map base and defaults such as all road type avoidances. The GPS should have alike set-up.
Jay