Pros
Job roles aren't really defined, so you can make a niche for yourself doing a lot of different things, I guess... Pay is not awful, although not as good as competitors. They pay lip service to diversity and inclusion.
Cons
Incompetent engineering management to the extent that it's unethical to sell as a service. This goes hand in hand with an opaque promotion system based on favouritism and undefined job roles where there's no knowing what you'll actually need to do. People can "make their own niche", but that just means that the people who are successful are salespeople first, rather than engineers. They paint over the cracks rather than tell the difficult truth. This culture comes directly from fellows right at the top of the company; it's deeply embedded and not just an isolated experience. This is the result of a structurally flawed organisation. The teams systemically compete against each other within the company, and all the blame for not having filled timesheets is passed down to individuals. You've got all the worst parts of being a contractor, paired with all the worst parts of working for a company. What are our bosses here for? As well as embarrassing engineering outcomes (yes, HS2 is as bad as they say, and Arup leaders can take a good share of the blame for that), the lack of process around structuring project delivery prevents them from defining job roles, and so they can't employ or promote anyone based on any defined criteria. This creates a culture of favouritism and secrecy which flies in the face of all of their talk about diversity and inclusion. They initially *seem* to have good intentions, but the shine wears off VERY quickly.