Depends on how much kit you want to install.
Just putting a sear in gives you about 75% of the benefits of the full blown kit and ( if memory serves) only requires popping the sear block from the frame after pushing one pin . ( Read: pretty easy). Changing additional springs and/or the trigger itself goes up in involvement but none of it is hard. (Much easier than a revolver IMHO) As mentioned, If you want to install a new safety plunger and spring, the rear sight needs to come out. That can be easy or hard depending on the individual gun and your availability of tools.
FWIW, I often get the results I want by just doing the sear and polishing the trigger bar and plunger on my M&Ps.

Check out youtube for lots of video's showing the process.

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Dave