i could be wrong, but from reading the description on the website, it is a two-piece design. it goes on pretty much the same way an ar-15 button would and then you just pop on the button.
btw, i couldn't find a video about the ndz install.
It would "seem", given the limited lifespan of o-rings plus it is hardly a solid connection (you can easily pull it off with just minimal finger effort it appears), that people would be losing the engraved button part left and right... but I guess it has been working out well as they sell them. I love extra detail piece on my weapons like this, but this is one I decided to pass on personally.