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 sometimes trigger sears do not sit exactly perfectly once first installed, this may cause a little sticking in the mechanism. If that occurs, repeated use will eventually brake it in and it will be fine. Steel is strong stuff so be patient, it may take a little longer to brake in then other softer seers.