I read, watched and spoke on that site and to the very head coach who give those lessons; Hamilton makes more than a simple coaching job: he forms you as a coach, enable you to evaluate and analyze the game so you no longer need someone to look after you for your game to improve. His advices are not limited to the "what to do", but he reasons with us, push you to see "how to" and most important "why to"... Really, if you follow each and every of his free lessons, you are ready to make of your tennis game a solid one, fundamentally sound and efficient in every aspects.
His Premium course is a notch above it; he takes it further and discuss tactics, strategies, positioning and give you an in-dept course about footwork. Those, he covers them briefly in the previous kind of lessons, but he'll be very specific and will take examples on the ATP tour, analyze them and explain how anyone can apply that to their weekend game. That's what he says he presents on his webpage if you search a bit.
If it worth it, I cannot tell since I didn't even have a sample from it, though I did read his preview and presentation, however, I used his free lessons to change my game. I had the humility to erase and reset myself down to zero and start all over on solid basis which FYB provided. Of course, I have a background in video and match analysis, I read and thought about bio-mechanics in sport, but it doesn't get away what Will does and what his team does: it brings ideas and concepts to reflect about and it allows a player to enhance his level of play a lot.
I am confident about this new part since I advice anyone to give Will and his free lessons a chance; I often quote him or add one of his pages as an example. He still is very friendly and close to his subscribers, paying or not, and he will be glad to explain you what you will gain from it if you would speak to him or send him a mail. Go on his website and ask him in person if my advice is not enough!