I have used a dynabar on my Nitrous shorts. And have done for years. Makes life so much easier.
I now use a waist harness, because I've been riding a Surf Board for the past year. I save the seat harness for TT or boosting days. I don't like the squeezing of my ribs when I'm jumping with a waist harness.
So for me, Surf Board & waist harness with JayBar and seat harness when I'm twin tipping, with dynabar. Or if my back is playing up, I will use my seat harness.