Pros
Fair compensation - I'm not sure if this is a pro or a con. They will give you a fair compensation based on your market, however, you will definitely get better offers from other companies. Challenging work - TransferWise is growing and with that comes scaling problems. You will learn a lot about how scaling should be or should not be done.
Cons
Autonomous Teams - Somehow this is a little bit of pro, although in TransferWise's case teams are so autonomous that it affects cross-team communication very badly. Teams will move fast without even considering how it will affect other teams. Politics - Even though, from the outside, it seems TransferWise is a startup, I would say that it is not and there's a lot of "politicking" going around. "No drama. Good karma." is the least true of TransferWise's core values. There is a lot of drama, it's just that people tend to not call it out.