Mikeintightpants sent these pictures, along with some information:

Mikeintightpants writes,

“Four hands are better than two. SuperPTC high security handcuffs — from China. These beauties have a very complicated unlocking procedure. My sincere thanks to a friend in Hong Kong who sent them to me for my collection.

“The key is in two parts, connected by a short spiralled “lanyard.” Each part of the double-ended key has to be inserted at each side of the cuff at the same time AND both ends of the key have to be inserted the correct way round in the respective sides of the cuff as the pins are of different lengths — they have to fit into those small holes that you can see along the cuffs — then, to complete the unlocking, that small knurled slider has to be operated. Not easy to do, even with two people doing the uncuffing!

“Definitely not suitable for self-cuffing!”

Thanks, Mikeintightpants, for the pictures and the information!