Pros
I interned at COS in 2016. I gained surprisingly legitimate experience. I was put on a real project and had a lot of freedom, and I ended up writing considerably more lines of code than I did at my 2nd or 3rd internship (this was my first internship). Center for Open Science's internship is definitely closer to real world experience than a lot of bigger companies that pay more and look more impressive on paper. Really awesome workplace environment. Even though they don't pay their employees very much, they've still been able to implement a lot of the cool parts of start-up culture.
Cons
I made $12.50/hr which is the lowest paying software internship I've ever heard of. Although there were some good engineers at the company, the overall quality of engineer was poor, and the company was not managed very well. This is to be expected from a non-profit software company run out of Charlottesville. Having a cool mission can only make up for so much quality.