I tried to use one with a rigid Surly Instigator fork without success. It kept sliding up the steer tube, I could not get enough tension in to it to pre-load the headset. It will ultimately depend on the inside diameter of the steer tube.
The benefit is that you don't have to use a regular star nut, which can be a pain to fit. Plus, when you switch forks, you just take the complete assembly out of the steerer and you put it in your new fork.
Also, the cap and cap bolt can be used with a star nut. But you can't use the nut or cap separately, they have to be used together.
I believe that you could use a regular bolt + cap on the head doctor steerer assembly.
I use an Azonic Head Lock. Works awesome. These are designed for 1 1/8" forks so to use for a tapered fork I got a washer at the hardware store that fit perfectly over the bottom flange of the Headlock and fit the outer diameter of the bigger tapered steerer tube.