I installed one on my D18 about 6 months ago. Like you, I was kind of worried about it, but I did some research and got some advice here, and it installed perfectly for me. I looked for the thread I started here, but I guess it was over on the old site.
Before I drilled, I found Martin’s schematic on the recommended button location and followed it. I also taped the heel and used a depth guide on the drill bit. I ordered the little felt washer along with the button and I think that was a good idea. It allowed me to snug up the button without digging into the wood.
You might want to make sure the button won’t be in your way if you have a cutaway or play up the neck a lot. Also, make sure the guitar will fit in your case once the button is installed. My heel button made a new indentation in my case, but didn’t stop me from using it.