circs-bamboo and plastic, mostly so that the girls in class (ME!) could figure out which one to knit the next round it.
As for two sizes, check gauge. Be careful with that. My LYS owner was telling us (in particular me, the Addi junkie)since I wanted to knit on Addis that Addis do not ''match" other needles in terms of size (diameter)-she says it is enough to make a difference and recommends either using no Addis or TWO Addis rather than, say, a size 5 Bryspun and a size 5 Addi, whereas two size 5 Addis would be fine. (hope I'm making sense....)
Let us know how you do!
(Sorry, brain fog here. I can use two Addis but given my A.D.D and my first sock on 2 circs, she thinks I should have two different looking needles).
Okay, I'll shut up now.
Hope my rambling helped a little.