One of my members got one of these to have something to play with while he does his "real" project. First impression was that it was over-engined, and needed very careful throttle control to prevent it looking silly. With a more sensible motor choice both the whining and the overly exuberant performance could have been cured by Thunder Tiger, but a 15 volt 545 is a cheap drop-in replacement. He started thinking seriously about that when he tried fitting a fuse, and popped a 20A car type fuse. I was left wondering if the motor was one of the infamous e-bay Johnsons of ill repute from a couple of years ago. I suppose they had to go somewhere......
The whining is a result of the way ESCs work - they switch on and off many times a second, which kicks at the moving part of the motor and passes pulses to air. We hear these as a whine, but some ESCs run a much lower rate of pulses, so we just hear a rumble, some are so high a rate that we just dont hear them. At anything other than full throttle, when all the pulses merge into one, the whine will be there, but will be at its loudest when the pulses are so short that the motor is not turning (i.e. minimum throttle, as you have noticed).
In that boat, with the right motor, it should be good for an afternoon's sailing.