Pros
Some of the most interesting projects I've ever worked on have been with BAE Systems Applied Intelligence. Deep technical skills are prized, and well applied. There's a significant effort made to enable engineers to do their jobs, although this varies by team. If you find yourself in a good team then you can get a lot done. Pay is pretty good, and while it can't compete with banks it is close enough. The company is supporting of WFH, where possible.
Cons
Teams are, by the nature of the work, somewhat isolated from each other. Diversity is poor, but this is probably indicitive of the overall industry, not just AI. At the end of every financial year there tends to be a feast to famine transition as annual contracts come to an end, and our customers fight their internal processes for a month before renewing them. Some IT systems are a shambles, typically the ones that a thin veneer over SAP.