There is a lot of misinformation about nickel here.
It CAN be applied directly to steel-most factories do it this way. Bumper plating shops use a copper underplate.
A nickel finish won't hide imperfections in the metal, it amplifies them. Nickel can be used to hide a silver-soldered joint, but pitting is much more obvious with nickel.
Properly applied nickel is not prone to flaking. If the nickel surface is compromised and the gun is not cared for, rust can form in the unplated area and spread under the surrounding nickel, causing it to flake.
Nickel is much more durable than bluing, and protects much better.
And-before someone says it- Hoppe's and other solvents won't affect properly applied nickel.
Take this for what it's worth. I do nickel plating.