Pros
I came to the company not expecting much, but I've been blown away with how receptive they are. The UK engineering office may be small in terms of number of people, but the talent in the room is amazing, I have learnt so much and I continue to learn new things everyday. The CTO is very understanding and will help you progress in your career, whether that means letting you take on more responsibilities or if its simply taking a course.
Cons
Dealing with product managers / project managers is very hard. However that stems from the fact that the experience of project management isn't there, and since this is still a relatively young company that is something you can forgive as they are still learning the ropes. That being said, sometimes the deadlines for requirements to be developed can be rather unrealistic.