I like the line mount too but it is a pain in the ass to setup and I also had 1 bad line tangle.
My first time, I used only 1 rubber as advised then my kite stalled after a jump, got line tangled and the mount broke in half. Camrig sent me a new one
I have a high Y setup so the lifeline is not an issue. I set up all 4 rubbers now and haven't had any issues last couple of times i used it. Launch can be sketchy, ideally you need one guy launching your kite and one launching your gopro lol
One time I had 4 rubbers thing on and got a small tangle the camrig setup slid down the lines but didn't break. So i don't think the lifeline would be an issue even with rubbers on, if the kite pulls you enough it will slide down easily. You don't need so much force to pull the lines through so I don't think i would be an issue.
Though it is possible that line mount with or without all rubber make a big line mess which would disable your life line.