Here is a link to a Baseball America article
discussing Constante and why he signed late. Apparently teams have shied away from signing 16 year old Dominican pitchers because most of them don't develop well.
Reports say his fastball has a lot of movement to the point where catchers have a hard time catching the ball. Sounds good as long as he can control it.
I saw a link somewhere in Spanish that led me to believe Constante is a converted outfielder.