I bought both of the Dreamz interchangable sets this last month and just love them! I had most of the fixed circular needles in older brands (decades old) and new bamboo circulars, but I had a love hate relationship with them. Seemed like no matter what the pattern needle gauge called for I ended up using 3 sizes larger.
Finally went to LYS and got the newer fixed Dreamz in a size to try and got a few others in different metals. I absolutely loved the Dreamz wood needles and found if the pattern suggests a size 7...I am usually able to knit to gauge with the same size 7. I was amazed that changing type of needle could make such a difference.
SOOOO I went and bought the longer needle set as well as the short needle set that comes only with 16'' diameter.
I found that if I want to do socks with 2 circular needles that I can use the short and the long needles because the long cords fit the short needles too. I plan to get the bulky add-on soon, but doubt I will use that much.
I loved the Dreamz so much I just bought fixed 40-47in 0,1,2,3...so I now have all the sizes I might need in the Dreamz...and I have all my older circulars that I can give away to my granddaughter as her knitting skills get better, since she isn't fond of my Dreamz needles for some reason. She prefers bamboo and acrylic oddly enough.
Good luck picking out needles. It is much cheaper to buy a set than individual, unless you know that you can't use most of the sizes because of how tight or loose you knit.