MLB.com's take on Purke
When healthy, Purke is one of the most complete pitchers in the Draft class. Taken in high school in the first round of the 2009 Draft, Purke didn't sign with the Rangers and went on to TCU instead. After a stellar freshman year, he entered 2011 as one of the top college arms as a Draft-eligible sophomore. He throws his fastball comfortably in the 90-95 mph range and can even touch 96 mph. He has a plus curve that has the potential to be even better and a slider that has the chance to be plus as well. His changeup is fringe average, giving him four pitches that he will mix and use to work hitters and keep them off balance. Purke is very confident on the mound and can be best described as a finesse lefty with plus arm strength and power. He was, however, shut down with shoulder bursitis this spring, leaving his status very much up in the air. Considered to be a tough sign even before the injury, it remains to be seen who will take the chance on his arm and his signability in June.
They also have an advanced scouting report here