A few comments on handcuffs, as they appear often in my homepage...

This is the  'standard-model', with a chain between the cuffs, and a reliable double lock.

This is a pair of handcuffs, where I've cut away the chain.
At first it might seem like pure madness, but there's a logic to it
This modification gives you the opportunity ( i.e. by 'self bondage' ) to get the handcuffs on, in a proper way, to have then locked tight enough, but not too tight, and finally to engage the double lock, before having them out of sight..
Then, having completed the correct mounting procedure, you simply apply a short piece of chain, and 2 small padlocks, which by the way, are easy to close with one hand.

 
This one is a dangerous specimen, at least for self bondage, as you'll NOT be able to insert the key into the keyhole, while cuffed !
Apart from that, it's a fine set of handcuffs, especially due to the fact, that you'll be very much handcuffed in these ones. The hinged shape will i.e. stop you from clapping your hands, if they're inserted 'from either end'
 
These handcuffs, however, are straight forward dangerous... 
The main problem is the very poor quality, as well as the poor design of the ( so called ) double lock. Most often, the double lock mechanism will not work, the lock will jam, and/or the keys will simply break inside the keyholes.
Most unfortunately, it's these, you'll find in the porn shops, but they are quite easy to spot, so here I'll give you the 'key' to avoiding them:

1/ (The purple ring) this lever is the only way to operate the double lock. this means that during play, you'll have to stand absolutely still, in order to prevent the lever from dashing around...

2/ (The red ring) The keyhole is an easy way to spot these handcuffs, this is a sure chekpoint, along with

3/ (The blue ring ) -the keys. If you see a handcuff-key, with these 3 rings on the top, my suggestion is, tat you depostit the keys along with the handcuffs in the closest recycling bin.. deep down. 
The keys are made from a very cheap alloy, which will inevitably break during use, and that's rather quick.

-and then.. please don't get fooled by plush coverings, or names as i.e. "Love Cuffs".. it's all just different wrappings for the same old garbage..!

'Double lock'.. and what's that all about..?

Handcuffs are in general designed to work like this: You insert the wrist, push the cuffs closed, and then you're locked in - meaning that you'll not be able to open the cuff without the key !
This is an excellent way to do this, and then.. Now, if you're cuffed, and squeeze the cuffs, they will become tighter and tighter and... if the double lock hadn't been invented.
a proper double lock operates like this: Upon closing the cuff around the wrist, you insert the tiny 'pin' on top of a good handcuff key, into the opening, ( most often found on the side of the cuff ) in order to engage the double lock.
The locking mechanism will now be 'blocked' in order to prevent the cuffs from 'closing' any further, regardless of how you pull or push them. This means that they will not squeeze your wrists, beyond what's intended. ( And that's exactly why the cheap cuffs is a piece of [...] ).

Here you see the key-pin inserted into the double lock opening, thus engaging the double lock.

Now, there's one more trick to the double locking mechanism. When you ( inevitably ) want to unlock the handcuffs, you'll need to open the double lock, prior to opening the cuff. This is most often done by inserting the key into the keyhole, and then turn the key clockwise, to disengage the double lock, and then counter clockwise, in order to open the cuff ( but DO check this before you apply the cuffs ).

Good handcuffs are wonderful toys, but just to put it straight, they are designed to hold you, until you apply the key, and if you ( for one reason or the other ) cannot insert the key into the keyhole, and turn it, they will do exactly that !

Gode håndjern er fremragende legetøj, men vær lige opmærksom på, at de er lavet til at holde folk fast, og hvis du ikke kan låse dem op, så er det det de gør !