Pros
Due to it being a start-up company, the environment is different from larger companies in that you actually get to meet and work with everyone in the office. Everyone is working hard to see the company succeed and it shows in the successes. Also as an intern, they offer so many opportunities to learn new skills.
Cons
Need to be fully in-person (which is not the end of the world) but obviously this means that if you are not already in the area, you would need to relocate.