The correct fans should be used with the correct type of controller. The Swiftech rep on here has said that using Voltage control on PWM devices can potentially do damage to them.
It is unlikely to be true that PWM devices respond to voltage control better than devices designed for it. A lot of PWM devices, including fans, actually have a narrower working voltage range than their conventional counterparts so in fact they would provide less control.
If you compare the start voltages of these Noiseblocker fans;
The PWM versions at the bottom will only go down to 6V before they stop vs a little over 3V for the conventional versions.