From the start I saw in Springfield, I would say Roby is legit. He hit 100 on his opening pitch and blew everyone away. He gave up a run on a opposite-field double on a pitch that the hitter was late and fooled.
He reminded me a little of Greceffo when he was going well. Both arms appear to me to be better than Woodford, Rom, McGreavy, and Thomas by a clear margin.