My family raises Hancocks, and while I was in college I did a paper on that line of breeding.  So my info comes from experience and research.  There are two lines that go back to Hancock, one is the line that makes hardy horses with speed and buck.  The other line creates hardy horses that are very cowy, no buck, but don't have the speed of their counterpart.  We have keep several of the horses we raised for our own purposes.  I do most to the breaking and have never been thrown by any of our colts.  For the most part our horses are pretty cold blooded.  After their first thirty days or so anyone is able to ride them.  I have a little stud right now that I am afriad to cut becuase if he gets any calmer I'm afraid he may die.  I also have a mare that is the same age who is very manageable but very hot.  She has never bucked but she has tried to attack things that spoke her while I'm riding her, like my rope, or tin cans that roll past her.  We do have other mares that are kid gentle but are quick to work.  These are horses that sometimes go for 6 months to a year before they are rode and we have no issues.  I could go on for pages debating this side of the coin and provide a dozen more personal stories on different horses, that weren't buckers.  But I have often heard people say they had a great Hancock, after they got their first buck of the day out.