You didn't ask about the Onlyfire setup, but since I got one recently and have it going today, I thought I'd add a pic and a comment. The Onlyfire ring is a combination rotisserie/pizza oven/smoker expansion. I don't own the other 2 options you did list.
This one fits over and around the kettle bowl like the lid does. It's a pretty good fit on my standalone 22"kettle, but my performer is slightly out of round and it takes a little playing with to get it to lock on.
Right now I've got it in the smoker expansion setup with the bottom vents closed, top vent barely open, and there's still enough air coming in between the gaps to maintain 225F at the lid. No foil is in place anywhere either, but it's not unworkable at all.
The pizza oven door thing is what sold me on this one. The small gap left around that door is probably where most of my leakage is coming from. If the door is removed to do pizzas, the temps will soar as one would expect.
I've only used the rotisserie attachment a couple times and for about 5lbs of meat at a time, but the motor that came with it plugs into the wall and didn't appear to struggle while I was using it.