From section 3.3.6 of the 1999 HGFA Towing Manual:

Bridles used for aerotowing hang gliders are either "one to one" as shown previously, or may be a shorter bridle which is connected to the pilots harness at the chest or shoulders.

When aerotowing intermediate hang gliders, a "one to one" bridle is essential.

When aerotowing lightweight gliders the tow line is attached to the release using a metal ring only (with a weak link between the ring and the tow rope).

I and others have towed single surface and intermediate gliders with the pro tow ("...shorter bridle which is connected to the pilots harness at the chest or shoulders") bridle/release system. I've done this many times. Recently at the Dalby Big Air I used the "Moyes" type system for towing an Airborne Fun 190 behind a Dragonfly, but I have often used my pro tow bridle to tow the Wills Wing Falcon 3 - 170, Wills Wing Sport 2, Wills Wing U2, and Aeros Discus. Pro tow bridles are routinely used for towing intermediate and single surface gliders by pilots who have sufficient experience.

This is the part of the HGFA towing manual where it is made explicit that the weaklink needs to go between the pilots' system and the tow rope. It is expected by this description that the pilot's system ends in a metal ring and that the weaklink is supposed to be metal ring at the end of the pilot's system and the end of the tow rope, which I suppose, is supposed to end in a metal ring also, although this is not explicit here.

Section 3.5 shows the rings (although there are numerous "problems" with this diagram when it comes to aerotowing):

My experience and that of many other pilots with aerotowing in Australia and the US is with using the pro tow system that does not match these requirements. So, in spite of the fact that these statements are being made in the HGFA towing manual, it appears to be the case that they are having little to no effect in the field.

I look forward to any response from the HGFA or other interested persons. Again, I have a direct personal and minor financial interest in the issues raised by this discussion.