I did try the back bridge and hindu squats based on the written description on his website, YES I can feel them! I should do them consistently. I don't have any injuries so I should be all right. I also do handstand push-ups against a wall, I started out barely going down, now I can go down about halfway (I am a female), and I don't need the wall for support as much. I am a big fan of doing things upside-down, I also enjoy doing headstands (free form in the middle of the floor). :-)
Perhaps if I ever get a job I will order some of his materials, I like his way of thinking.