Pros
The product is quite interesting to work on. The office is fun. You get to try new things so it's a good place to develop new skills. The people are the best thing about the job. The CTO is very smart and if he has time for you then you can learn from him.
Cons
Work-life balance is non existant. Lots of late nights and working weekends without recompense and the pay is low compared to other positions in London. Office politics is a huge problem. The CEO has his favorites (also hires his friends) and makes it clear to the company who is favorites are because he tells the company every Monday. Those star employees can do no wrong and they can also blame you for anything that goes wrong and the CEO will automatically take their side. Some of the CEO's favorites know this and take full advantage of this. Strange cult around the CEO and Hadean. "Hadean comes first" not the people. If you are not part of the cult then you'll never be considered a favorite and you'll be chased out of the business. Senior management not good at ensuring workload is balanced and there is lots of crunch on projects. Constant pivoting also means workload and stress is always higher than it should be.