If this helps anyone, here is what I would consider a 'proper ma bu'

http://alexng.net/fsuwushu/reference/horse2.jpg

This is not:

http://www.dekungfu.com/images/sifu/Horse%20Stance.jpg

Holding the first picture for 1 minute will give infinitely better results than holding the second for ten minutes. Try both, you'll feel the difference immediately.