Check local statutes
When working as a security guard, I was to provide my own cuffs. I only used them once off duty, on a meth freak who stabbed me after I rebuffed his panhandling attempt on the way home from work ($2 paring knife). My fault letting him get too close. I'm glad I had a less lethal option, and even more glad that I had training in takedown and cuff use.
If you wish to carry cuffs on a regular basis, check local statutes, and get trained in their use. Learn how to apply, adjust, and double-lock them. Carry a spare key in your wallet, or somewhere you will always have it with you.
Takedown training is key, be aware that you will be putting yourself at greater risk by approaching or combatting a subject.