Yes… YouTube is one of the best resources for math teacher! Why? During the Pre-YouTube years, you had to know a dynamite math teacher, attend workshops, conferences, or seminars to see demonstrations of (non-virtual) manipulatives in action.
You can ask any math teacher if they have seen or come across blocks, graphing calculators, protractors, compasses, die, spinners, or the whole frickin’ ETA/Cuisenaire catalog where training was not supplied and DID NOT HAVE A CLUE TO USE IT!
Now, as math educators, this gives us a great reason to create videos (if they are not in YouTube) of HOW to use those pentominoes, 24-Game cards, Ken-Ken/Suduko puzzles, integer chips or even tangrams that has collected dust in our closets and drawers buried underneath posters and miscellaneous teacher crap.