Rode the slumbercoaches many times on the Broadway and Silver Meteor. Great for a growing family. Wife and I usually booked the double slumber and either same for the two kids or one each single, since they liked having their 'own room'.
Meal service was 'on your own' but never a problem getting seated in the Dining Car.
I found the slumbercoaches quite comfortable, and certainly very reasonably priced.
Only thing I liked better, for the price, was some early Amtrak 'single rooms' which Amtrak priced same as roomette. The Empire Builder sported a dome with those types of rooms early on in Amtrak.
I miss them!!!
When in Europe, to this day, I mostly booked their version of the slumbercoach ...the Couchette or Liegewagen. Never ever have had a problem nor an 'uncomfortable' moment.
Bring back the Slumbercoaches!!