Metal knitting needles are made by many manufacturers and were the most common
type until fairly recently. I'm trying to be impartial here, but the only advantages I can
see are relative indestructibility, low cost, and a clicking sound as you knit (if that's what you like).
A digression: In the old days, when metal needles were all there was and my husband
was in graduate school and always studying, I would often hear the injunction, "Can't you
knit more quietly? That clicking is driving me crazy!" Now, with plastic, wood, or bamboo
needles, I'm happy not to hear that anymore.
The negative qualities of metal needles are that they are cold, hard, and inflexible.
If you have any problems with your hands such as Arthritis, Tendonitis, or Carpal Tunnel
Syndrome, you certainly should avoid metal needles.
To be fair, there is a type of metal needle made by Addi Turbo that many knitters
swear by. They love the slippery coating on these needles, which speeds up the knitting.
Try these if you really want to knit really fast.