Advantages:
  bright color under etching (due to the nickel)

Source:
    This steel is typically used in nuclear containment vessels in which the high nickel content confers better resistance to radiation decomposition (compared to mild steel). I purchased a large quantity from a company in Texas in the form of 36" x 2" x 1/4" strips (torch cut). Since I try to maintain a high carbon content in the billets, I use this material sparingly. I typically hammer it down to ~1/16..1/8" thick and include a single piece in the mix.  As a result, I don't expect that I will ever run out of 203E.