Nice heads and shading. The head from Marc's course seem like it could use a few adjustments.
Like the middle of the lip, looks like it leans a bit to his right and the middle part is a bit too pointy:
The nose seems like's being pulled downwards a bit, feels like it could have a bit more folume to the fron and reduce the shadow on the middle part a bit.
Overall it's looking good. My first head from Marc's course didn't look nearly as good as this. That's some really nice shading done.