I agree with what you say. I have improved in my flexibility and have been looking for ways to challenge my flexibility more. I especially like the ones against the wall. I will use them! I actually already use all of the dynamic ones you mentioned, along with jump squats through a full range of motion, it helps with the explosion from the hole. I would like to point out, something you alluded to a little bit, that while there are definite basics for proper form, like chest up, knees out, etc., perfect form is going to vary depending on the individual. Everyone is different in the their make-up and somethings are just going work better for one person than another. And that is something everyone has to figure out for themselves. I tend to have a wider stance, just right outside of my shoulders, low-bar, toes pointed out, and a medium-wide grip. It works for me!
