Pros
The people. All of the engineers are fun to work with, smart, and really help each other out on projects. The shared knowledge of this company is fantastic, and easily accessible by everyone in it. The engineering team is led by true engineers that have moved into management, not managers without engineering experience. This holds true all the way up to the CTO/COO, deep engineering experience is a hallmark of the senior staff at Security Innovation, and that's a huge benefit to everyone on the engineering team in my opinion. SI is a casual working environment, but everyone still delivers their work very professionally. We aren't as much on the far-end of the "party spectrum" as some other security companies, and I'm okay with that. That being said, the company still covers the entire engineering team heading to DEFCON every year, and engineers are welcome to choose additional conferences and professional development curriculum as they see fit. Everyone is encouraged to engage in personal research projects, and given the resources to do so. I believe compensation at SI is at least on par with or slightly better than similar companies in the area. Bonuses should be expected for excellent performance, as well as stock (both options and direct, depending). Good quality full health/vision/dental coverage is standard, 401k, all of the normal benefits.
Cons
New employees are (generally) expected to hit the ground running - that is, we hire security engineers and expect them to be accustomed to this work, and there isn't usually much ramp-up before you're on a project. Usually this is fine, but I could see that as being surprising or even challenging to people at first. That being said, people don't seem to leave SI as much as I see people jump around other similar companies.