Those style buttplates are usually made out of sheet metal that is hammered into shape. Occasionialy you will find one that is a single piece, but most are two pieces that are rivited/brazed together at the heel. Forming a buttplate in that manner is not too difficult, but getting it symmetrical about a centerline (for me anyway) is just about impossible.
Most of the steel parts available today are investment cast copies of parts that were originally available in brass, so there are very few steel parts that have a proper style. If that is of no concern to you and you just prefer the look over brass, then go right ahead. It is your rifle and you are the only one you have to please.