YOU have to determine how you can use the needles you purchase. Some people may be able to use them to make some things and others may not be able to make the same things on the same needles. Just my opinion! 
Anything thatās flat on circs? How do you mean?
Simply put ā¦ anything that you would knit on straight needles ā¦ a sweater, a scarf, or anything else that is not circular (so it is āflatā) ā¦ you can do on circular needles. Make sense? Socks and hats (and anything else done in the round) could probably be done with them too.
How?
Back and forth just like on straight needles. You would turn the circular needles around when you get to the end of a row, just like you turn the straight needles around.
I prefer circs because I would rather by a set of circulars than a set of circs and straights. Why buy straights when you can do the samething on needles you already have?
Itās good in that you have a variety of needle sizes all at once without buying individual needles. You can use the long ones or put cords together if you need the size for blankets. As for making hats, yes you can, it may be difficult with the 12" cords, but you can use longer ones in a Magic Loop, or a variation I use where you only pull out the loop on one side instead of both. Thatās how I can knit sleeves and hats on 24 and 29" needles. Or you can rig up 2 needles and knit in the round too. You would put a needle tip of the size you need on one end of 2 cords, and a smaller tip on the other end. Only use the right size end for the actual knitting, it doesnāt matter if the other end is smaller.
Wowā¦kind of sounds like rocket science right now, but it vaguely makes sense. The package of the needles arrived today, so maybe when I get it out to play with Iāll read back over suzeeqās accomplished understanding of the needle system and how to get what you want out of it!
Iāve got to tell you though, I donāt think I will EVER knit a blanket (watch- I will end up knitting just that!;-P) I do want to knit a sweater for myself, though, and tank tops and ooo, my project that I got my forum name from that I have YET to complete!!- a bikini! And a dress would be fun, skirts, hatsā¦I hope this system becomes useful to me!
Baby blankets arenāt too big, about 30-36" across, but you might want to put a couple cords together for that.
I have two sets of Boyes and one very old Susan Bates one. I prefer the Boyes to the SBs, the difference being metal needles as opposed to plastic ones. I use them for everything these days, I rarely use straights any more. Though I am putting those new ones from KP on my wish list. I have converted most all my straight patterns to circular with no seams unless absolutely necessary. What wonāt fit on my circs go on my DPNs
I bought the Boye Needlemaster from a KHer and I love them. If anyone wants to sell another set, please let me know.
I just wish they came in smaller sizes.