Hardware of software firewall for a server

Looking into moving from a software to hardware firewall. Any big drawbacks? Any big positives?

We have standardized on Calyptix which has a lot of functionality.
Positives:
1. Separate out the firewall function in a different box that is likely to be harder to attack
2. Get to charge the customer for another box or service. I usually try to get an MSP fee on the box. I have heard others give away the box to close an MSP sale.
3. Frequently any competitor of yours will not know the box you are using.
Negatives:
1. One more thing to learn.