Actually, OPTIONS is the 'type' of interchangeable circular.
However, KP OPTIONS are now available in 3 materials: NP, HARMONY, ZEPHYR.
Here is their ADVERTISEMENT banner here at KH:
Because NP (nickel plated) was the very first OPTIONS available, a lot of people use
the term OPTIONS when they really mean OPTIONS NP, nickel plated.
I've got full sets of NP and Harmony. Well worth the investment.
I have 3 sizes in the Zephyr acrylic, however I didn't invest in more. They perform much like the Harmony's do but they are much more affordable for someone entering the world of interchangeables. I recommend Zephyr's to anyone needing to spend as little cash as possible.
But if cash is not a problem...my first recommendation would be the Harmony's. They knit fast, warm, and not too slippery. I'm a fast knitter, usually preferring Addi Turbos/Clicks and Signature (circular) Needles...but I can get a lot of speed out of the Harmony's just fine. They are nice when I need a needle that isn't a sharp as the Signature Stilettos, and not as round as the Addi Turbo/Clicks.
I use Harmony's more than I thought I would! It is a great needle! I'm still amazed at the affordable price of all 3 (NP, Harmony, Zephyr) of the KnitPicks Options interchangeables!
I don't know how they do it!