Beagle
the use of ILS is not covered during the PPL syllabus of trianing, whereas the use of en-route navigation aids is
I am not sure that is necessarily a good rule because e.g. the DME isn't covered in the PPL either, IIRC. (Rather silly, as few navaids are simpler to use). Does that mean a PPL cannot legally use a DME? Surely not!