Pros
I get to speak to, work with and learn from C level management on a daily basis. Great relationship with my manager and other colleagues. A very young office (and company) so I've made genuine friends. They expect a lot from you but are fair about it; if you work hard you will see rewards. I've been allowed to move between departments to find my feet and have now settled in a role where I've been able to mould my job to what I like doing and am best at. I have been told by our CEO in EMEA that there's "always" room for progression. It's a really big successful start up which means that you'll need to be proactive if you identify something that could be improved upon. We're still regularly coming across scenarios that we've never thought of before due to the success and massive growth and management are very open to sensible, thought out solutions that would make life easier moving forwards.
Cons
No HR rep in London so it all has to go through very busy managers.