Well, I just bought the stretch series and thought I'd share my experience with FS yesterday: wow, ow, and yes!
I have decent hamstring ROM (in a standing pike I can get my hands flat in the floor without a warmup), but I knew I needed work in other areas..and this program is hitting them! Achilles, ankle, and hips/quads will be especially benefit from this protocol.
Those calf raises were BRUTAL. I did ballet from 10-16, but I have apparently lost a lot of what I gained there. I struggled to keep pace, couldn't make all the reps, and my ankles started rolling out all over the place. YIKES. Also, I can hardly walk today my calves are so sore.
Thank goodness everything else feels fine.
My other biggest struggle was the narrow hurdler (have since found the advice I need to modify in the forum--thanks guys!) and the one legged hamstring stretch against the wall. I couldn't get it right so that I was stretching my hamstring. Kept getting pain in the hip of the supporting leg. I read about this pose on the forum, and I'll play around with it on off days, but I may have to post a form check later to get help.
All in all, really excited to see my body improve with this program!