I use flossing techniques often, although what he's demonstrating is technically not a flossing technique but a tensioner technique. The techniques are useful, not a cure- all but definitely help with a subset of patients with certain sciatic symptoms. I usually use a traditional flossing technique that maintains constant tension; the knee extension and ankle dorsiflexion combined with neck extension then the trunk and neck flexion along with knee flexion. Tensioner techniques like the one shown are not as in vogue, this was more of an old school approach used more 10-15 years ago and have to be used with caution as the sciatic nerve doesn't always respond well to such an aggressive technique.