IMHO, the tubes don't do a particularly good job of circulating. Way in the past, I had a Wonderwood stove, the box-within-a-box style that U.S. Stove has been making for many years. In other words, the stove itself was surrounded by a sheet metal shell on all four sides, with the shell a couple inches out from the sheet metal of the stove. So in function it was kind of like the wall protector you made. That really did some circulating! Don't get me wrong, I'm not saying the DS Machine is a bad heater, just not a wonderful circulator. I set up a 14-inch pedestal fan to blow across the top of my stove -- not ON the stove, just above it -- and it vastly improved the circulation and the comfort in the heated area.
The tubes DO add significant surface area for heat transfer, but the limited convection air rising through them doesn't take full advantage. If you attached a manifold to the bottom of the tubes and ran fan-forced air from bottom to top, you would probably draw a lot more heat from them.
As far as "which stove" -- figure out how many BTUs you need, and go with the model that will produce it, remembering that all manufacturers exaggerate their stoves' output. DS Machine is no exception. Maybe the stove will produce its rated BTU at a flat-out maximum burn, but not as a practical everyday thing.