I just got off two JL flights (one in C from HAN-NRT in the SS8 SkySuite and one in F from NRT-JFK). I have to say I was really worried going in, since I'm the sort of person to turn off my heat in NYC right before I go to sleep even in the winter because I get too hot even on the lowest setting, but I had no issues on either flight. I actually needed my blanket on both flights because I got cold. Admittedly I wore gym shorts and a t-shirt on the HAN-NRT leg since no pajamas were provided and I didn't put on the pajama top given in JL F, but I almost never put on long sleeved shirts to sleep in. I think it might just be a YMMV situation combined with the lack of vents to regulate if they do set the temps too high.