This unique design was originally called Hiatt UL1 but now the new incarnation is the TCH 850. They are nickel plated, weigh around 490 grams and fold!  The clever bit is that when they are unfolded they lock up automatically and are more like a conventional rigid handcuff like the 840.  You need to use the key provided to fold them up but when folded they are arguably more user friendly because they don't stick out so far.  These comply with the latest NIJ standard  This is the black version with all the usual TCH features like backloading and double locking.