A jam chuck? I don't understand. In my experience, A jam chuck is a chuck that is super tight fitted to the work and you "Jam" the work onto the chuck. Using an expandable mandrel is a bit different than a jam chuck. I think it would be closer to TBC than a pin chuck. When you use the mandrel, you use the tailstock to support the back until the very last minute. Then you tape the front of the work to the headstock and finish the bottom off.
If you use a pin chuck, you are risking OOR pens in my opinion. If your pin is too big, it won't fit right and could easily warp the tube shape or even crack the work. If it is too small, the tube and work will not be in the perfect position for turning, therefore it will be OOR.
I agree about the whole "It's just another tool" aspect. In fact, I have a couple of pin chucks myself. But at the same time, If i know of a better, easier, faster way to do something that also saves me an hour or two of cutting, filing, and shaping a bolt, well that is the way i go. It personally makes no difference to me, as I have already found my favorite technique. I was just asking because i figured there was something about a pin chuck that maybe i didn't know that makes it better. In my experience, A pin chuck would be more of a last resort than a preferred method.