Sat through the RM from BTS documentary for my mom since she wanted to watch it and mostly my takeaway (since I'm not really that into BTS) is that it was really fascinating to see all the casual code switching/language switching going on, because generally in scripted media it's usually avoided.
Anyway, if you like BTS, I would recommend it, I am extremely not a documentary person like that or much of a BTS fan so sitting through it was mostly for my mom.