Two have a variable speed setting while the third, cheaper, version has a fixed speed.
Is it really necessary to alter the speed of rotation ? I quite like the look of the other, and I will save a reasonable amount of money in the process.
There is absolutely no advantage in fitting a speed control to a rotary machine, as it needs to be revolving as fast as possible.
As soon as the battery starts to die and the machine slows down, the deception will be spotted by incoming pigeons.
It is one of the main reasons why birds shy away from spinners, they simply see the arms going round once they get in close.
That is why I favour the Hypa-lite whirly – the arms are almost invisible from 50 yards away.