I totally agree that yoga is beneficial for people with back pain, but am super-cautious about any one-size fits all approach to therapeutic yoga... there are so many causes of back pain, and individuals respond very differently to exercises. So I think it's awesome that resources are available to get people started on a yogic journey, but believe that there's really o substitute for guidance from an experienced teacher, preferably in one-on-one or small group context if there are pre-existing injuries or conditions.
Just my 2 cents worth!