My buddy runs a small feedlot outside of York, Nebraska and he bought one of those portable units about two years back. He swore by it for sorting out his heifers before they went to the packer, said it paid for itself in the first season because he stopped sending his best marbled ones to the wrong buyer. Then last fall he scanned a big black steer that showed off the charts on the screen, so he kept it back for a private sale and the carcass came back Choice minus on the rail. He still uses the thing, but he tells everyone it's a good guessing tool, not a guarantee, and he always goes back to running his hand along the ribs before he loads the truck.