I took one of his courses a couple years back. It was in differential topology if I recall correctly, we worked through topology up through Whitney's embedding theorem. It was nice. It really is just for fun, the "homeworks" he gives are really up to you to do since he doesn't collect them, and there was an "exam" but as long as you showed up to the classes and didn't doodle the whole time it was fine (he really doesn't want to give an exam, he just feels he has to in order to justify the grades he's obligated to give out). All this to say it's really up to you how much you want to get out of the class, if you put more effort in you'll learn more and he's always willing to discuss stuff.