My honest advice for someone who is evaluating Cisco Secure Firewall based on my experience would be that if you can get something else, go for something else. If you are going to use it, then use the CLI because the GUI is not usable. If I had the choice, I would not be using Cisco Firepower or ASA on top of it because in my opinion and the opinion of my colleagues and my management, it is not the best device for the role it is playing.