I have a set ... used them for a bit. Found that the clips were leaving some holes in the fabric where they snug into the channels.
I thought it was a very clever system, had high hopes.
What I'm doing now - I sewed a strip of velcro onto my leaders to work with the Leader Mates - I made a set of secondary leaders, with the softer side of the velcro.
I sew the secondary leader to my quilt back top & bottom (long basting stitches), and just press the velcro on the secondary leaders, onto the leaders on my rails.
I had no luck at all pinning - found that I couldn't get the dang thing straight, and kept picking myself.
I'm quite enjoying the secondary leaders I've made, is working ok!