Small Arms Factory (SAF), Lithgow, New South Wales, Australia
First model has two obvious distinguishing features. A single oblong link and the bow has a milled groove on one side only.
Next it had a groove both sides and 2 links. They were used extensively in Australian and New Zealand Police and Corrective Services.
There are other differences in the keying, see photo. All have the Small Arms Factory logo but only the later ones seem to have the words "Small Arms Factory, Lithgow, N.S.W." stamped on them.
Left is the first model where each half of the cuff is keyed the same. Next is the NZ Army model where each half is a mirror of the other. Third is a New Zealand Police (standard model) which is keyed from the other side of the cuff. All are modeled after the old style Peerless cuff.
The SAF-LOK is a whole other cuff made by the same company under different owners over time. The number of variations is a bit blurry due to the number of links used, color of the bow, markings on the bows etc and it is unclear if these changed slightly due to different suppliers of some components ie links. But there are also differences in the mechanisms to what is in the patent and some variation in the rivets to the bow. I don't think the subtle variations to the Saf-Lok makes a "New Model" but certainly changes to the mechanisms would even if the bows all say SAF-LOK MK.1.but I'm no expert on mechanisms.
Then there are the more recent SAF-LOK models, Standard, Hinged and limited trial model Bed Cuff which is a single cuff on a long chain and link. I am less familiar with recent models.
I hope that helps.