FWIW, I did an unpaid internship at a patent law firm during the summer of my 1L year. At the time. there was 1 managing partner (attorney), and about 10 "interns," some of whom were law students, some of whom were patent agents, and some of whom were still doing their undergrad. There were other attorneys associated with the firm who worked as "of counsel." Since I wasn't being paid, I elected to get credits through my school (which ended up costing me money since I had to pay tuition for the externship credits). The managing partner was an inventor, and had several issued patents, and more patent applications in various stages of the filing process. Most of the work we did was internal, meaning we primarily worked on the managing partner's patents, i.e. infringement analysis, responding to office actions, preparing economic damages reports, etc. Some of the patent agent interns actually worked on client matters, i.e. drafting claims for new applications, responding to office actions etc.
Given the ratio of interns to supervising attorney, the level of supervision was pretty low, although the managing partner made an effort to have weekly one-on-ones with each of us, and I believe the patent agents who were working on client matters were given more supervision.
I ended up earning 3 units that summer, and I stayed on part-time during the fall of my 2L year, getting paid a small hourly wage. Overall, I'd say it wasn't a bad experience, and it probably helped me get my next jobs. That said, I don't have a tech/science background, so I realized that patents were not for me.