It's tougher than nickel, and it's not a coating. It's a plating process.
Here's the description from the site:
http://www.mahovskysmetalife.com/Metalife%20Finish%20Page%202.htmThe Metalife finish, otherwise known as SS Chromium M, is our most durable finish. Metalife looks like stainless steel, but has a hardness of about 71 on the Rockwell "C" Scale, which is even harder than stainless steel. It is guaranteed not to chip, crack or peel when applied to metal in good condition, and it is highly rust resistant and holster-wear resistant. It requires reasonable care and is guaranteed for the life of your piece.
Also, the Metalife has a maximum build up of only .0002. This means it will not affect the tolerances of even the finest fitted parts. Unlike some platings which coat the metal, the Metalife plating process fills the pores of the base material to form a molecular bond.
We recommend Metalife on guns that are in excellent condition and free from pits. Pitted pieces can only be polished to a certain degree without changing the contour. Also, pits have a way of cratering metal, making it nearly impossible to process down deep inside of them.
Metalife is successfully applied to aluminum frame automatics as well as steel. When we receive an aluminum piece, we must first apply a plating of our high phosphorous electroless nickel. The Metalife process is then applied over the nickel giving the piece the ultimate in durability.