He's from windup, has turned sideways and the leap occurs as part of his motion with hand break. It is after leg lift but before rotation. It would not be possible for him to do anything other than deliver the ball to the plate.
Re advantage I think most coaches would see it as a fault, rightly or wrongly. My kid (LHP) is being told to d/c a similar , less extreme motion in his delivery, because his instructor feels it is detrimental. Who knows.
Also, as this is from windup, presumably there would be no runners on. Has to be continuous its in the middle of his delivery, could not possibly be construed as an attempt to deceive a runner even if it was from stretch with runners on.
Interesting tho. There was a major league signing a few years ago that threw like this . Cannot recall name. Anyone else know it?