You mean that you don't like his mechanics? Prior's inverted-w form wasn't flagged as a problem until after he suffered his injuries, and it's still questionable whether they really were bad mechanics or just an attempt to explain his injuries.
I suspect, though, that the Nationals will be very careful with him and use the latest biometrics to ensure his mechanics are perfect. I would definitely have drafted him...he has like four pitches that grade at plus to plus-plus and tremendous velocity.