It's a calculated gamble on MR's part. If he is confident that he will go in the first round then he should go. While it's a gamble, I am sure there are ways to make a fairly educated decision. It's also a gamble to stay in college another year. You cited Raab and Allen and how there are positive aspects to staying in college. That is true but I'm pretty sure MR has no other occupational ambitions other than playing pro ball. If he has a well above 50/50 shot at the first round then he should go.
Its a huge gamble, and I don't think his odds of being a first round pick are better than 50/50.