THe problem is pretty simple. Co2 on a hot day is about 1500psi, and can be 2000+ if your tanks is overfilled.
Most macroline is rated for 500psi, and some is rated for 800psi. Most fittings are rated around 500psi.
Generally, its barely enough to safely run hpa. The thinner stuff for LP-output tanks, and the thicker for HP-output. I'd never run it on co2, unless downstream a vented regulator.
But to be fair, lots of people will say they have used it for "years with hardly any problems", and you can sometimes find stronger line and fittings.
But you reach a point where you have to question why its important? Braided stainless is far stronger, and flexible. Its just not as convenient. If you don't like the looks of braided, and willing to accept some risk, that use the macroline. Microline is a better choice, as its stronger (given the same specs), or setup a hardline. Hardlines are always sexier.
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