In general cervical headgear wearers seem to use two different kinds of straps, one where the facebow is connected to a metal loop (or what you should call it), like in

http://community.webshots.com/photo/163187086/259831642avWnSK

and some where they are connected to some kind of plastic modules, like in

http://community.webshots.com/photo/163187086/230222216QTHreG

Is there any reason for this? Do they have different uses, work different on the jaws etc., or do they work the same way? To me, the second type seems far more uncomfortable than the first one (neck/head mobility).

I was told that the (older) conventional, elastic strap with a metal loop each end could be uncomfortable for some patients.

The more expensive type with spring modules delivers a more constant force, is more comfortable for many patients and the section at the side of the face is less visible. It is hugely more expensive than the conventional elastic strap.

A further development has a ptfe tube around the neck within which is an elastic; the connect to the Kloehn bow is by a quick release clip; this is (allegedly) the most comfortable; permits easy head movement; and is least noticeable.

Some orthodontists still prefer the Interlandi headcap because it fits entirely onto the cranium rather than the cervical region.