I'm wondering about the chain thing also. I bought some and gave them a try. I would say they are useless because I did use them once to pull my sons car out of a ditch.
For what my opinion is worth, forgo the chains, they screw up your form when it really counts. Please, please do not take that dive bomb advice, stay under control and feel the weight. Truthfully, I do not think your form is as bad as you think. Your ass goes back nicely and you are using your back. Don't get caught up in using too much back, they are strong muscles and if you use them they will help your squats.
Follow up with gtl's advice on another video.