There was a great article on the Handi-Rifle in either Handloader or Rifle magazine about a year ago - tested with barrels in .357, .44, and .223. It performed reliably and accurately with all three. (The .44 particularly rocked for accuracy, though only with bullets of 265 grains or less.)
They talked a bit about accessories for the gun, e.g., receiver sights, and I think slings.