If your attaching your leadcore directly to your release your going to have a bad day sooner or later. That might work for a little while but it will break eventually. I would run it all out and attach directly to the backing. If your lucky it will only break and you'll lose gear. If your unlucky it will break on a 20+ pound king.
We run 7' on our rigger rods. I'm not a fan of them but the kiddo's love them. They are worth there weight in gold to let the little guys handle the big salmon "all by themselves".
I think it looks very interesting. I have it, just haven't gotten it on the lake yet. If it doesn't work i guess it'll give the kid something to do on the boat anyway. The price is right for sure if it works.