> the markings are mostly superfluous? You're basically doing the same motions in a regular intersection.

The image linked, yes. However I've never seen one quite like that in the US. Instead where I'm at we have a small circular barrier in the center of the intersection (and some very eye catching reflectors) that you actually have to drive around. It's a very good design (imo) because it physically forces vehicles to slow down and swerve so there's no way to inadvertently blow through it at speed the way that sometimes happens with a 4 way stop on a long straightaway in the dead of night.

The space requirement is only slightly higher than the one linked above, still much less than a proper full size roundabout. It's basically a cement barrier sticking 1/4 of the way into your lane.