I had a subscription to it for a year, and I loved it. It's really fun to watch various people ride and teach.
I feel it's no substitute for having a good dressage instructor right there in person, watching the rider ride his own horse and giving personal instruction.
But that site is really great. And the videos are very good - quality and content and breadth. You can really learn a lot!
I don't have it now, but not because there was anything wrong. I try to sign up for one thing each year, that is, something different each year. This year, I got FEI-TV.