Pros
Amazing People (really): Made lots of friends during my time at OM who I still keep in touch with regularly. There are good people in there, everywhere. Design Thinking: With a big emphasis on design - OM makes you think about your work in ways other places might not make you. As an 'ad writer' I left with so much more knowledge about UI/UX. Great Culture: A product of them putting good people before anything else. Intercompany Play: Being sister company to Bensimon Byrne and Narrative - you get to move fluidly across agencies which helps keep things fresh. Beautiful Office (for when that matters): Just such an inspiring place to work in. So nice it made me not want to WFH. Independently Owned: Your boss is your boss, not someone across the sea. It's nice creating personal relationships with the people you work for. They're also great.
Cons
*disclaimer, not really a con, more of a preference thing for different folks* Loose-r Structure: This can be a pro or a con depending on what type of system you like to work in. OM promotes an entrepreneurial attitude - allowing you to own what you're working on. You might enjoy this or you might not.