Pros
Arbor is full of good, smart people, from top to bottom of the company. The company culture is laid back with an eye towards maintaining a good work-life balance. It is led by mostly engineers who have risen up through the ranks, and has a nice mix of veterans and newer employees, including an active intern program.
Lots of nice perks, such as unlimited vacation time, snack wall, frequent sponsored lunches and tech talks and fun outings, game days, arcade machine, pool table, etc.
Employees are encouraged to incorporate their interests and passions into the job as much as possible, and to feel free to move about to find their best fit within the company. Everyone is expected and trusted to be responsible and doing what is needed for their job.
Cons
Haven't seen any yet, Arbor has not only survived but flourished through two acquisitions and seems to have found a great fit within its new parent company, Netscout.