What a set is
A set of needle tips in a range of sizes, a few cords of different lengths, and a way of joining a tip to a cord — a screw, a click or a clip. Any tip on any cord is a circular needle of that size and length, so a set of ten tips and three cords stands in for thirty fixed circulars. The tips come off a finished project's cord with the stitches still on it, so a cord with end stoppers is also a stitch holder.
The sums
A fixed addi circular is about $16, and a full addi Click set — a dozen or so sizes with several cords — costs what ten to twelve of them cost. If you would otherwise buy that many circulars in the sizes the set covers, the set is cheaper; if you knit everything on a US 7 and a US 8, it is not. The honest count for most sweater knitters is six to ten sizes across two or three lengths over a few years, which is where a set pays for itself — and the case gets stronger if you knit lace or blankets, which want long cords in odd sizes.
Who a set suits
Knitters with several projects on the go, who park one on its cord and move the tips to the next. Knitters who change needle size mid-project to hit gauge, or who swatch a lot. Anyone who travels with their knitting and wants every size in one case. And anyone who has already bought the same US 8 circular three times in three lengths.
Who it does not
Sock knitters: most sets start at US 4 or so, and the small sock sizes come as fixed needles or a separate small-size set. Knitters who use one or two sizes for everything. Lace knitters who want a particular tip (the addi guide sorts the tips) — check which tip the set has before buying. And beginners: one fixed circular is the right first purchase, as your first needles explains, and a set is for when you know what you reach for.
Where a set can let you down
The join. A fixed circular's tip and cord are one piece; an interchangeable's meet at a join, and a join can catch yarn or, over time, work loose. addi's Click system has no screw: the cord pushes into the tip, twists and locks, and cannot unscrew while you knit, which is why it is the one we stock. Length. A cord's advertised length counts the two tips, and standard tips are 5" each, so the shortest circular most sets make is about 24" — no 16" hat needle. addi's short Rocket tips are 3.5" and get down to 16". Small sizes. Tips below about US 4 are too thin for a join; addi Click runs from US 4 to US 19, so sock sizes stay fixed needles. Losing a tip. A fixed needle is one thing to keep track of; a set is twenty.
What to check before buying
Which sizes and how many cords are in the box; the smallest size and the shortest length it makes; what tip it has (rounded or lace); and whether cords and tips are sold separately for when you want more.
The addi Click Starter Set we stock
It is not a full set, and it is not meant to be. The small red case holds one pair of each of addi's three main tips — a Turbo pair in US 7 (4.5 mm), a Rocket pair in US 6 (4 mm) and a bamboo pair in US 8 (5 mm) — with two cords, 14" and 22", and the connector that joins two cords into a longer one. Three tips, three sizes, three working circulars, and a hands-on answer to "Turbo or Rockets or bamboo?" before you spend on a full set in the tip you like; the addi guide is the paper version of the same question. Every Click tip and cord is also sold on its own, so the Starter Set grows into a set one size at a time. The Click Hook Set is the same system with Tunisian crochet hooks on the tips, for crocheters, and needs cords bought separately.
The middle road
Many knitters end up with a set for sweaters, shawls and blankets and a handful of fixed needles for socks and hats — the 16" circular in a hat size and a 40" in a sock size that the set does not make. That is not a failure of the set; it is what a set is for. The circular length guide says which lengths matter.