Here is my design for an easy to print 3D model of stylised handcuffs, heavily inspired by a popular video game about strandings... and deaths ;)

Supports can be a pain but totally doable, I've used 2.5mm x 5mm magnets for both cuffs to open and close them, these I press fitted with a vice with some glue, you can see the holes on both clearly, for the "dagger cuff" I ended up only installing one side of magnets as this turned out to be sufficient.