I have them...

Am getting back into using them again, particularly the Zen, 30 minute yoga routine, its really helping loosen off my calves and glutes which have become appallingly tight from cycling.

I think if you can slot them in and do it regularly then you will see some gains in core strength which, although I would love to think it doesn't, does make a difference on the bike.

They are a bit "home made" feeling but that doesn't bother me at all. Last winter I dabbled a bit with the 30 minute Yoga, fix the back and bonus core workout (ouch ouch ouch) - I'm going to try to stick to it this year, particularly the yoga and the core workout. Just need to pump my stability ball up

I also find his e-mails quite informative when I remember to read them.