420J2 was never intended as a blade steel. Its used primarily because its very inexpensive.
* Edge retention is on the low end of mediocre, but there are worse steels. none of those worse steels are blade steels though, and 420J2 has the worst edge retention of all steels commonly seen in blades.
* I think its MAXIMUM achievable hardness is like 54 Rc. most 420J2 blades are 52 Rc or less; why would the company pay good money to harden a steel they only purchased because of its cheapness? The up side of this is that it is easy to sharpen....but unless the company actualy spent the cash to harden a "junk" steel, then you will likely only be able to get a toothy working edge.
* It is VERY VERY corrosion resistant. It almost impossible to make it rust unless you let it soak in harsh chemicals for a long period of time.
* It is very durable. Its low hardness makes it unlikely that a 420J2 blade will break, unless its design is structurally unsound.
In short, it is a poor overall blade steel, that has little business being used for knives, outside of a dive knife. MOST, but not all, knives made from it are of inferior quality.