In short, this absolutely works and from ~half year of experience, is completely reliable under extremes that you ought not to find typically, including some unintentional high-speed collisions. I can’t speak for the long-term durability of said coupler box parts in a decade from now mind you, but so far, the parts I’ve made have been completely reliable. I’ve been doing this at some scale (i.e. ~60-70 cars/locos all with 3d printed coupler box components of some configuration or another), so it’s a large(ish) sample size.
Others, like
@GaryHinshaw , have been doing this sort of thing longer than I have.
I’m using just plain old “AnyCubic Basic” resin, and I believe that has been what Gary has been using as well.