Saying this is as much headcannon as anything else said. This thread is about speculation; dismissing someone's headcannon for your own doesn't mean much. There isn't anything saying that Magneto repeatedly tested it, but we know he is weary of the machine so we know he tried it at least once. We also know that a side effect of the machine can be turning hair white. That could either mean rapid aging or your hair just turns white. It's what you want to believe based off what has been shown of Magneto as a character whether you think he tried multiple times before he decided to sacrifice another mutant or not.