Pros
The office is a lovely place to be. It's beautifully designed as well as filled with a great bunch of people who are always happy to drop what they're doing to help you. Office culture great, company socials happen often enough, everyone lunches together and can always find a couple of people for a tipple at the end of a long day.
The company is great at giving architectural assistants a sense of ownership within projects, often being placed on a project mid to long term and not just resourced to different projects every other week and are given a bit of autonomy when it comes to the design process.
Cons
Like most practices, overtime is expected and depending on the projects you are working on and their stages, this can be for extended periods of time in some cases.