Thanks guys!
I like everything about the stuff except for the aroma while cutting. LBD is correct about a stiffener underneath, if I cut away at the top for a replaceable insert I'd probably add one below. I have a lot of 3mm aluminum strips from VME chassis face plates.
When I had a ZCI made from 1/2" MDF, it was stiff, but the area around the kerf blew out quickly, Aluminum would take the beating much better.
Duck also reminded me with his ZCI link that I have an MJ Splitter bought many years ago that I've never installed.
I also have some left over HPL flooring which is about 5mm.