Pros
Steady work if you can get a full time slot at a good site. The corporate office is relatively hands off once you go through hiring and initial training. Relatively understanding for time off, but sometimes you may not get your hours back.
Cons
No real upward mobility outside of site supervisor. You will miss holidays and weekends until you are a senior officer. Hourly pay means most employees would rather work than go on vacation even though your vacation is paid out every year. Persistent shortfalls in personnel levels occur yearly requiring employees to "volunteer" for overtime. Reality is that with some supervisors if you are one of the two guards off that night you'll be voluntold to cover shifts. Healthcare plans before and after Obamacare are some of the worst out there. Prior to the AHA healthcare coverage was $100/month but covered practically nothing but yearly doctors visits. After there was no plan available until several months after. Even then the plan is $250+ a month and from what I've heard doesn't cover much more despite costing twice a month.