I've seen many times (and been told many times) that 550 cord should not be used for suspension, but I believe I've seen people using zing-it. Zing-it's specs are in the same category as 550 cord, so I don't understand.

Can anyone fill me in on why zing-it is better, or am I confused?

Also, I realize that zing-it and amsteel DON'T stretch (much) and that paracord does, but is this inherently "weaker"? If 550 cord is doubled/quadrupled up, shouldn't it be just as strong as amsteel?