Pros
It's a startup. Anyone who has never worked with a startup needs to check their ego at the door. That can be a really big con for some but it's definitely a pro for me. Roles can and do shift, but the work is rewarding and the people are great. One of the biggest perks is that the founders DO THE WORK. It's not always pretty or easy but they are here doing it just like the rest of us. Also, we all work with clients to address their concerns and actually pass along feedback/advice so developers can implement new features on the software to accommodate when the need arises. As a result, the developers are constantly tweaking and updating the system to make it better, per client feedback.
Cons
It's a startup. Depending on your personality or work style, that may be a huge drawback. The "security" aspect here isn't the same as somewhere like Merrill Lynch or another large company because it's a young company (still in its first year). Customer feedback and program changes definitely drive the direction of the workflow. One minute you will be doing one thing and then you will be asked to do another. It's the nature of the beast.