Braided metal hose in wall
This flexible supply line hose is often called "braided stainless steel" tubing, but the SS is just armoring. The hose inside is some sort of rubber or elastomer. It will not last as long as copper, PEX, etc. and I must assume is not code approved for placement inside wall cavities. For one thing the connections are plastic seals which dry out or compress over time. They can only be used where they can be inspected without opening a wall.