I have this same set of interchangeable needles. The cords are a little stiff, but for regular knitting in the round and flat knitting, they work fine. Just be sure to use the key to tighten up the join, and the cable should stay in place pretty well.
These needles are slippery, which is great for some projects and not so great for others. For example, I started out using my more expensive bamboo needles on one project but then had to switch to Boye because the yarn just would not move freely. I find that my stitches are not as even when I use the Boye needles, but generally this little annoyance blocks out and the benefit of having the yarn glide across the needles far outweighs the wonky stitches.