Jeet kune do has become exactly what Bruce Lee dearly wanted to avoid: a 'system'.
He originally began to experiment in other styles simply to develop defenses against them in his original style of Wing Chun. Then, he began to study them for techniques that he could employ successfully. He laid these ideas out in the form of concepts, and taught them to students of his Wing Chun school. Many of his theories were actually drawn from his studies of Philosphy, principally Krishanmurti's teachings.
Then, he named it. And immediately regretted it. (Yeah, HUGE Bruce Lee fan, here. Read everything he ever wrote, watched everything he ever appeared in.)
As it stands now, JKD can be a devasting system taught by true masters of the concepts and philosophy. Or, it can be the same cookie-cutter crap you get taught in a McDojo's.
I say, give it a whirl, and if you don't like it, just bow out with something like, "It's just not for me. After all Bruce Lee said 'Your Way is not my Way. Your Truth is not my Truth'."
The quote from Bruce should let him think that you put a lot of thought into JKD. He'll be flattered, and less likely to be touchy about it.
But, you may want to go to the Library and see if they have a copy of Bruce's Tao of Jeet Kune Do. It's a compilation of his various notes and thoughts on the ancient and honourable art of the Sukiyaki Nose-Toss. Good reading. Thought provoking.