Ventajas
upper management is non existent so it's basically you left alone, figuring out how to best service your clients. Many previous employees have to left to start their own agencies, SEOP is a great training ground for entrepreneur mind sets. It can be as easy or as difficult as you want it to be, you have leeway to leave and come as you want and don't be surprised by the lack of professionalism; it's run by young guys and it's very much what you would expect. You have the freedom to expand your skills and grow and learn about the newest trends in digital marketing, just beware of the sales team.
Desventajas
The way they sell their services, is not based on capabilities, it's very much whatever the client wants, they can do. Sounds like a good business model, but not when you're often not given the tools to succeed to please your client. Word of advice always be straight up with your clients.