Pros
You do get to work with real clients which is cool.
Cons
They WILL use you. It's part-time, unpaid and they overwhelmed me with work citing that they just "really liked my designs best." Their entire infrastructure sits on top of unpaid interns. In weekly meetings, the CEO would brag about how he won't take any investor's money because they're doing so well, which was so uncomfortable to hear as someone who was being overworked and unpaid. Also, they constantly tried to pressure me into completely plagiarizing existing designs. Please avoid them.