I have a few of the Rivo 1920s heavyweight cars. I do like them, they just look right to me, but I think they're a tad oversized when compared to say an IHC heavyweight. I have not compared it to a Spectrum or Walthers HW yet.
These cars have the coupler mounted on the trucks, so they should go around 18" curves as long as you're pulling. If you're backing up, this kind of setup is ripe for derailing, because the force is on the trucks, and not the body.
Speaking of which, I think they come with horn-hook couplers; you can replace them with Kadees if you buy a conversion set. Or, an alternative is to go with the McHenry drop-in replacement. Or, do like I did which was to body-mount the coupler. But, if you do that and do prototypical spacing between cars, there's a good chance they won't handle the 18" curves any longer. Mainly because the cars are too close together and the outswing is too much.
Kennedy