If you own a KJ KC02 (a.k.a. KJ Works 10/22) then you know its a great little gas blowback carbine.
If you have started planning or actually upgrading it then you are probably thinking about increasing durability for either general longevity or specifically to handle continuous use of higher power gas.
Whatever the case, replacing the various components with full blown steel parts is not a bad idea at all. Of course, it is also good to know that you can buy replacement parts if you need to and these particular replacement parts just happen to be a step up in the toughness department as well.
Do bare in mind that a steel piston is a serious amount of added weight over a lighter material and so while it would not be worth it if running on HFC134a / Duster gas, it would work with Green / Top and almost definitely be a good idea if you plan to run Red gas or CO2.