They also work well on passenger trains, as long as the train doesn't need to be switched. Put a knuckle coupler on the front of the first car, and maybe on the rear of the rear car, and use Rapidos in between. Appearance doesn't really matter, as the diaphragms hide the couplers anyway. The Europeans even have close coupling with Rapidos, which won't work that well with most of our knuckle couplers.
The problem with that is that most modern American passenger car models don't have a Rapido option.