Pros
Interesting product in an attractive space with a lot of potential; smart and knowledgeable people. If you like coding you will get a lot of freedom and autonomy to do just that. It will suit people who are driven, motivated, creative and don't mind "getting their hands dirty" . Working style is fairly laid back, there is no corporate noise or bureaucracy overhead, it's just really about getting work done. You will not get much social life here as work is remote but there are off-sites organised yearly in different parts of Europe which are just simply fun.
Cons
Typical for a startup - it can get busy and chaotic. As a consequence, depending on your discipline, you might end up with poor work-life balance. High demands on technical skills and time means it's not suitable for everyone. As it is a small start-up, you need to chase your training and career development yourself. Working individually most of the time might suit some people but I found it a bit difficult.