I just finished listening to the Baseball America Podcast from 9 December (it's free) in which they offer their commentary for the Rule 5 Draft.  Here is a brief summary of what they had to say about Mason Tobin (starts just after the 24 minute mark):

• If BA were drafting, they would take Tobin.
• Love his arm strength and upside (upside was the first they mentioned).
• Plus velocity (96 to 97), plus slider.
• Wowed the Angels big league coaching staff in '09.
• Matt Eddy from BA was saying all along that the Rangers would draft Tobin (guess they weren't all that interested in Scott Diamond, Anuery Rodriguez, or Elvin Ramirez).
• Only has 40 innings in three years of work.
• Shoulder surgery in '08, TJ in '09, and a clean up procedure this year.
• An impressive pitcher when healthy.

All of their comments were really good.  Besides, you already subscribe to their podcast, right?