Pros
It has the atmosphere of a mission-driven small company with a real community feel, but with all the perks and benefits of working for a big tech company (Google / Alphabet). Amazing gym, food, facilities and colleagues too. There's not much cynicism internally towards the company's goals or leadership, which generally creates a positive, inspiring and optimistic environment to work in. You don't have to be a machine learning expert either, they hire normal software engineers to work on all sorts of projects.
Cons
Not many to speak of, but one common reason people leave is because they are offered a leadership position elsewhere which cannot be matched internally. It's also fairly common for people with leadership experience externally to join DeepMind as individual contributors. This is largely due to the level of talent DeepMind hires in combination with great retention - so progressing into leadership roles is often harder / slower than it might be at other companies. So I'd recommend working for DeepMind for a whole host of reasons, but if you're purely looking for rapid career progression into leadership roles - there's probably companies where you can get that faster.