I’m well into my learning sock now, and I have to say that like any method, the one oversize circ technique for knitting in the round (popularized by Bev Galeskas under the name "Magic Loop") has its plusses and minuses. But so do both the two circ method and using traditional DPNs.
Advantages will be mostly felt by newer sock knitters who aren’t used to working on DPNs. They include not having all those DPNs in the work, and not having to worry about them falling out in one’s knitting bag, or having stitches drop off the ends. Also, because there’s a moment where one can pull the yarn of the last stitch on the other side of the needle tight around the circ’s cable, it’s easier to avoid those corner ladders that can form if tension isn’t just right.
Deviating from the Galeskas method a bit, I found standard (round, Dutch, Vee) heels are a bit easier to visualize if?the flap is worked back and forth on one side of the piece, and picking up to form both gusset edge is done so that all heel-forming stitches end up on?one side of the circ. Depending on the depth of the heel and heel style chosen some reapportionment of stitches may be needed just before the heel is started, so that one side of the?circ carries only the stitches needed for the heel flap, and the other carries the rest of them destined to become the top of the foot. After the heel flap is done and the gusset stitches are picked up, the gusset decreases are worked until the foot’s stitch count around?has been reached. At that point if there are unequal numbers of stitches on the two sides of the circ they can be re-divided into equal parts so that toe formation is easier. Short-row heel production is pretty close to the same compared to DPNs, except that the heel unit is worked entirely on one circ half as opposed to being done on a unit composed to two DPNs.
For me however, the method presents a couple of disadvantages. First, I’m taking a severe cut in production speed compared to using five DPNs, as after each half-round I have to stop and thread the circ through the stitches on the needle so that the points are correctly placed for the next half. I am not particularly fond of the bit of wrestling needed to move the stitches back and forth over the cable joins at the base of the needles, and I find the first row to be particularly annoying, especially with the stretchy half-hitch cast on I favor for sock tops. Also very short circumference rows are more of a pain than wider circumference rows. I’m going to be sorely tempted to move my knitting to DPNs when I get down to the toe, rather than finishing out the piece entirely on the giant circ.
I can also see that extended use of a circ in this fashion is more stressful on the needle than conventional knitting in the round. I’d be wary of using a needle from a multisize kit in this fashion, were they to come in a suitably long enough length. I also note that most people are using very long circs (36" or 40") to knit relatively small circumference things like socks (although if only one sock was being made at a time, some knitters might be able to get away with one size shorter needle). These are expensive and can be difficult to find. Items wider than say hats would be difficult to do using the one oversized circ method unless a really long needle could be found.
The giant circ method is very close to the two-circ method in terms of execution. Both divide the stitches in half. In the giant loop method, the halves are separated by the teased out cable loop. In the two circ method, each half of the sock is on its own needle. Working methods are the same, except there is no teasing the needle back through the work each half row with two circs. To be fair, there is a moment of drop and hunt as the needle end needed for the next half row must be selected from the three danglers. Heels are worked in the same manner, with the heel unit being contained entirely on one circ. And both methods can be used for side-by-side sock production, in which both socks of the pair can be knit at the same time, each from its own ball of yarn.
To my mind, there’s one more clear advantage of the two-circ method over the one-circ method – while you do need to shell out for two needles, they needn’t be extra long. Many people may have two circs of sufficient matching diameter already in their collections. The two-circ method can be done even using two circs of unequal length (if the difference in length is very large, stitches may have to be divided in a smaller and larger group rather than evenly). Even using shorter or mis-matched circs there is less limitation on how large in circumference an item can be done than there is using the one-circ method. In fact, if one WERE to use two 40-inch long circs in the two needle method, one could knit a tube of around 75- 80 inches around (or bigger if the yarn/stitches were squishable). Of course, at the lower end of the range, the two-circ method has the same weakness as the one-circ method – smaller circumferences and fewer stitches are more of a pain than larger ones because there is more stop and grab or needle shifting compared to knitting time as a whole.
Finally, any sock pattern knit in the round – toe up or cuff down – can be used with both methods. Patterns written for five DPNs (four in the work, one to knit with) translate the easiest, as each side of the sock is equivalent to one of the circs in two-circ; or half of the stitches placed on one side of the giant circ in the one-circ method. Patterns written for three needles just need a tiny bit of tinkering to divide the available stitches between two needles. For sanity, I’d suggest dividing the stitch groups at the point between the ones that will form the top of the foot (the instep stitches that are not worked during heel production); and all others. In some cases this should be evenly in half, in others, there may be one needle at the sock’s outset that carries a few more than the other.
I’ll continue and finish out this pair of socks using the one-circ method. I’ll probably do another using two-circ just to keep parity. But being DPN-handy, I won’t be switching over to use either method for routine sock production. However both methods ARE handy tools to keep in one’s knitting toolbox. I DO use two-circ now quite often for knitting sweater bodies in the round, and find it a godsend for working two in-the-round sleeves side by side (no more "is the second sleeve long enough yet?" guesswork). I might use the giant circ method for hats or leg-warmers, but for something as narrow as a sock, mitten, or wristlet, it’s just too much needle manipulation for me.
To sum up – both methods are nice additions to one’s knitting tool set. Both have advantages and limitations. While both are useful (especially for the DPN-shy), neither is an absolute substitute for DPN skill for everybody, nor for every instance in which DPNs are commonly used. I encourage everyone to expand their skill sets. You never know when a left-handed wratchet-ended sawtooth crimper is required, and it’s nice to have one available when faced with that need.
If you want to learn more about these techniques I’d suggest Galeskas’ The Magic Loop: working Around on One Needle (Fiber Trends, 2002) for the one-circ method; and Cat Bordi’s Socks Soar on Two Circular Needles (Passing Paws Press, 2001) for the two needle method. Both books present these methods in well-explained detail, accompanied by patterns and sample projects. Both are widely available through general merchandise and needlework/knitting specialty booksellers.