Pros
It is a very good culture to work at. Much easier to make a big impact and be an important player in a young company than just a cog in a machine. You will be challenged which I think is a very big pro. You will also be surrounded by very smart people. This is not a place to sit back and coast. Everyone makes a meaningful contribution and you can always count on your team.
Kontras
This job is not for everyone. Sometimes it's a lot of work, long hours, and after hours activities. There is a good work-life balance but you are expected to do a lot of extra curricular activities like community service, and outside learning. Some people think it is a pro and some a con depending on who you are and what kind of commitment you can make. Some commit more that others and that's not frowned upon at all.