Hey guys, this is really nice, though quite expensive.
I've developed an open source wireless record-able follow focus and the code and schematics are absolutely FREE. Seriously. It means that you build it all yourself, but it works. No meaning to take anything from these talented guys and their work, if you want to really DIY, you're more than welcome to my blog to see for yourself.http://adisoffer.tumblr.com/
And you can see the FF unit in action here: https://www.youtube.com/watch?v=uXpLIT_GN6Q&list=UU7dAiT2E8yUWS2fIzELVX1Q