Well, if you really want to know the differences, there are many ways for enlightenment. Its not necessary that i repeat what you can find easily through friend google. I bet you didnt' watch the youtube video, did you?
If Philips is realy intrested to learn, 300 Dollar for a J3 shouldn't be a investment problem.
But just in short: All the trouble i had with the Gogear are vanished with the J3. It seems Cowon is able to write propper software in Korea. Sad enoght that Philips isn't.