Personally I have always considered that keeping as good a lookout as conditions permit is basic good airmanship. Reducing the sun's glare on your face improves your ability to maintain that lookout.
Mr Boeing is very good at providing sun shades which fail to fit tight up to the edge of the windscreen and the sun has an amazing knack of positioning itself so as to shine through the resulting gap.
My solution has been to buy a strip of green plastic intended to be used along the top of a car windscreen. Cut into 30cm lengths and used with three thicknesses it has light blocking qualities similar to that of the Boeing shades. The plastic is self clinging both to itself and to glass. When not in use it fits neatly in my briefcase.
(Lettering such as WAYNE or TRACY is optional.)