Dumb Question time:

What's the difference between one those Head-locks and a Hope Head doctor? Or rather, what's the practical difference, which is better?

Any extra/different procedures for using one? 

Head Doctors and Star Fangled Nuts are only for preloading the bearings the Stem bolts onto the steerer tube providing all of the strength you can remove the head doctor / star fangles / use another device to preload it,  the weenies run without anything there ( Including John J )

Head Doctor is easier if you get through alot of forks which I did for abit   But there still a pain to extract sometimes to reuse.

Also Star Fangles are a nightmare to get in with just a stick and a hammer...so a star fangle nut costs 50p but the tool costs like £12...a Head Doctor costs about £15 and looks sweet.

However, I've managed to snap a HD bolt...so be careful and don't use a long handled allen key if you're heavy of hand

SFN aren't load bearing though are they so they shouldn't fail.

HD's do mean you can have a cap without a proper tool and well they look pretty...