We are pretty comfortable with both metric and English simultaneously, though all our casework is metric. We don't think in metric yet, but we are starting to. The hanging strips are intended to be behind the cabinet back. They then don't show. Your side notch would still work.
Installation is a snap.
A 35 mm hole can be cut in the cabinet back upper corners with a hinge machine or notched. I understand what you mean about having the suspension blocks visible in open cabinets or cabinets with glass doors. You could used concealed suspension blocks specially designed and available for this reason. Sources for this hardware are PMI or H fele. They can answer all your questions regarding leg levelers and suspension systems.