This is a discussion which can drag on and on, as much of the procedures are based upon local regulation.
Having said that, as a matter of general airmanship, irrespective of whether or not the local procedures require it, I believe it to be good practice to always preface numbers with "Heading", "Flight Level". etc.
As an example a few years ago we overheard an aircraft at Flight Level 310 given a radar vector to "Turn Left Heading 310". His reply was "XYZ Left 310". The (predictable) ATC response was "Confirm you've left Flight Level 310".
No-one was hurt, but the makings of a serious event were there.
Remove the ambiguity, say it in full, it only takes a fraction of a second to say the extra word or two, even if not required.
Regards, and Happy New Year,
Old Smokey