I did a post bacc in Boston, used to live in NH, and got into Dartmouth this cycle. I worked at MGH full time while doing it and did the other pre-med stuff too.
I chose Northeastern for a few reasons. It's DIY, so you only have to take the courses you need rather than Tufts or something. It's affordable (sort of) especially compared to BU. I applied for and if I recall was rejected from Harvards Post bacc, although I might not have known about the extension school. I knew someone who did Harvard extension and said it was fine, I think you may have less access to resources compared to traditional students but I'm not sure. Also having the Harvard name but not actually going to Harvard doesn't actually get you any eyebrow points you know?
Northeastern was fine to good. I retook some core courses I needed, and branched out for some others. I found that because you're enrolled in the school of Professional and Graduate Studies, the tuition rate is lower but so are the number of courses you can take. For example, I needed about 24 credits to hit my goal, and because I was doing it for grade improvement I wanted as many "new" courses as possible to get A's rather than get an A chemistry where I used to have a C. By the end of my 2 years I was running out of BCMP courses which would improve my science GPA. I retook Biochem, Ochem, Genetics, and then took new courses such as analytic chemistry, human parasitology, epidemiology, etc.
Also being in the professional studies school means your classes generally meet once per week for a few hours which is ideal if you're working. The profs and students understood this, and many others were working full time as well. It makes the vibe less undergraduate which to me was a good thing. It allowed me to build better relationships with my professors and get LOR's from them, and network with classmates better. All the amenities I wanted from a school were provided, although I didn't use all of them. Library access, the email account, and ability to work in and with labs at NEU was crucial for me. Not to say this isn't possible elsewhere, but I had a good experience there.
Overall it was a very positive experience. I did have to chase some professors down about grades, and at times felt a bit neurotic about getting an A in every class at all costs, but I did and it paid off in the end.
Happy to answer more questions if you like! Good luck.
