Pros
Internship's primary responsibility is to organize a summer conference. Good stepping stone for underclassmen without much prior experiences but are looking for policy/government/legal internships.
Awesome people committed about criminal justice (death penalty, solitary confinement, drug law reforms, etc.). You will learn about the various criminal policy issues.
Opportunity to attend capitol hill briefings and panels. There's not much oversight to your work, and you really need to take the initiative to attend the events of your interest (criminal justice or others).
Very approachable colleagues. If you want to get involved in other aspects of legal issues (white collar, national security, etc.), you should reach out to people and get opportunities.
Great location: two blocks from the White House.
Overall, great place if this is your first internship. Very unnecessary if you are a junior or above.
Cons
Mostly grunt work (copying, filing, organizing, mailing, etc.). But the work isn't hard, and it's by no means long hours (average 10 am-5 pm). You'll have the flexibility to attend capitol hill panels/briefings.
Unpaid.
A very small pool of interns. In my year there were three-four undergrad interns including me and three law clerks.