I'm a current first year HES student and here is what I can say for the program:
1. Our chemistry professor and the structure of TF's and review sessions is the best I have ever encountered. Yes, I said it, the best. Tucci is healing wounds from an awful high school experience every week. It makes me excited for orgo (which is incredibly strange to admit).
2. If you don't ask questions or keep pushing yourself, you will not do well. The advisers, while approachable and invested in your growth, will not coddle you. Fixsen makes it very clear what he and the program expect from you. If you do not study or blow off the homework and labs, it will not end well. Stay on top of your work, forsake an active social life, and you will be pleased with your grades.
3. Classes are on Harvard campus. If you are in the diploma program, you will be granted a Harvard ID and access to amenities including the libraries and dining halls. Luckily, even if you are going a la carte, you have access to several on campus libraries including Grossman and Cabot. I have the ID, but prefer to go to the Cabot library over all the others.
4. It is extremely affordable and you can receive small loans to supplement your studies.
5. The classes are at night and the hospitals are hungry for research assistants and volunteers. If you'd like extra opportunities in healthcare, there is no better city than Boston.
6. I've formed some close connections with people in the program simply by attending class. It is a great idea to have a study group and web of classmates who share your schedule and drive to learn. I don't think these Saturday study sessions would be possible without a group of close friends and program mates.
7. Cambridge, for all its eccentricities, is quite lovely.
8. It is possible to live cheaply in Somerville.
9. While I regret the loss of my free time in changing careers, the program is relatively short and, should you wish it, leaves room for freedom in summer.
10. It is Harvard. The Extension School is part of the University as much as the Business School or the Medical School. The university states this explicitly.
Feel free to PM me with any further questions. Hope you find yourself in a position to decide between either program.