it's good to have one's research Confirmed by experts in the field.
here's one bike shop in atlanta georgia who Only sell the jamis trail xr 12" due to its geometry being suited for smaller riders.
http://www.intownbicycles.com/produc...mountain-bikes
The XR is our offering for that little guy (or girl) that's too big for a childrens bike, but not quite tall enough for an adult bike. We carry the XR in only the 12" frame size, although we can order any size. Think of it as an extra small adult bike.