I've known Jeff for a long time--used to go watch him play at Stanford and had the opportunity to work with him as both a player and as a coach.
The guy has an economics degree from Stanford, which may make him unique among tennis coaches worldwide. But aside from being smart, the thing I enjoy about Jeff is his openness. We've exchanged views on many subjects and think it's fair to see we've learned from each other, although we probably don't agree on everything.
It's great that tennis coaching has a young, passionate guy with his intelligence and playing credentials.