I did it to one of mine and I'm very satisfied with the results. I am however a little upset I had to pay $90 for just about the same thing from an APEX kit.
I've done the Burwell trigger job on a few M&P's, and I still prefer the APEX Hard Sear. All of my M&P's and all but one of the Burwell jobs is now benefiting from APEX technology.
You have the right idea in that the APEX is your fallback position if things don't go as you plan for the DIY job.