It did break, but not due to the weakness of the actual chain, but the chain link that we bought. Broke twice. It's made of thinner, harder stuff, and under big loads it fails. This was fixed for us by Marien (thank you!) at MMM, but his fix (using the same/most of the bits that broke) failed again later on. I'd suggest you avoid a chain link and get a chain breaker tool.

As for loads, I don't know, it broke from a landing the first time and under stress from flipping something the second time. It's 6mm size chain from technobots. They have it rated at 300kg tensile strength.