By this time, everyone knows that Jews for Jesus are not really Jews. They are Christians using the cover of their Jewish origin to fool people into coming to their proselytizing services.
Actually Alan, they use the Tanakh. It's not "Believe in Jesus. I'm Jewish." It's "Believe in Jesus. It's true. And it's a perfectly Jewish thing to do."
Now, as far as I can recall, Alan Dershowitz does not believe in the God of Abraham, Isaac, and Jacob. He does not believe in the inspiration of the prophets. Jewish believers in Jesus do.