I love my Nickel Plated Options, too! One thing about KP is they have amazing customer service. You won't have to send them the defective needle either. Just give them a call and they'll send out a new set.
There are some hints to using them...
-Use a grippy piece of shelf liner along with the key to tighten them. I've never had mine come untwisted since I started using that. And when you tighten them make sure you're not twisting the purple cable. Hold on to the metal parts only.
-When moving a lot of stitches along the cable to get them into knitting position don't yank the needles. I put a couple fingers on the cable at one end and slide the stitches the other way to the needle.
Since I've started taking this care I've never had a problem... other than the occasional needle or cable that needs replacing.