Screen-space solutions for something like this is not a good idea. The mask shifts as the camera moves, which you can even see in their video.
But, this is really simple and there are a few ways you can go about it. If you want to stick to something screen-space, looking at the “Normal To Curvature” code in the material is a good start since that does what you want, but doesn’t give you a mask. You can recreate it in the material editor though.
Another option, and the more stable one, is to use pre-computed masks for AO and edge wear. If you keep them in the middle range of values, without going too extreme on either end, you can use parameters in the material to shift the mask.