There's nothing wrong with an exclusive, it gives you an opportunity to execute well and align a strong public announcement with a high-profile client, if picked correctly.

However, six months is a little long. Typically, an exclusive like this is more along the lines of three months than six. In any negotiation, there's a side with more leverage, which I'm not able to determine with the limited information that I have. If it's you, I would pick what means more to you: A six month exclusive with more revenue or a 3 month exclusive with less and negotiate to that point.