Use dino-oil for breaking...your going to drain anyway and it will be full of little metal bits.
There are various opinions about when to use a synthetic and when not to use a synthetic, none of which prove or disprove actual data. AMSOIL fully warrants all of its products to be used from day one. Now, why use a ~$10 quart synthetic for break-in when you can use a ~$3 quart dino that your going to drain anyways? Doesn't make sense and that's why most will use the inexpensive stuff up front.
Most important practice during break-in, IMO, is let the engine idle to temp before riding. Once the engine is warm, take it a little easy for the first couple of runs, while gradually increasing the high RPM lengths. But again INSURE the engine has warmed up at idle first.