I just wanted to learn some hyperbolic geometry by myself. And I found this YouTube channel which has many lectures on many different math topics: https://www.youtube.com/user/njwildberger

Has anyone tried his lectures before? Is he any good?

Well he teaches at University of New South Wales so he isn't an internet crank/youtube messiah - whether his teaching style suits you only you can tell.

Well, I wouldn't necessarily say he's a crank, but he is an ultrafinitist, so while his videos may be decent overall (and I've heard they are), bear in mind that he's philosophically opposed to infinite sets, irrational numbers, and even finite numbers large enough that they cannot be physically represented. This goes against the mainstream foundations of modern mathematics. He's also attempted to reformulate trigonometry into rational trigonometry, which is very much fringe mathematics.

 

As an example of his position, a few articles expressing his views can be found at his page here: http://web.maths.unsw.edu.au/~norman/views.htm

 

I don't know how much all this will factor into any videos he's done on geometry, but it's something to look out for.

Well, I wouldn't necessarily say he's a crank, but he is an ultrafinitist, so while his videos may be decent overall (and I've heard they are), bear in mind that he's philosophically opposed to infinite sets, irrational numbers, and even finite numbers large enough that they cannot be physically represented. This goes against the mainstream foundations of modern mathematics. He's also attempted to reformulate trigonometry into rational trigonometry, which is very much fringe mathematics.

 

That sounds a bit weird.