Ok, thanks. Got that sorted now 🙂
Hopefully this will help others with the same dilemma.
I had read a post referencing the use of file://
notation which, apparently, is a red-herring.

Just for clarity to others, a local compliments.json
file should be located in /pi/MagicMirror/modules/default/compliments/ directory and referenced using only the file name in the config file.

e.g. remoteFile: 'compliments.json'