Soon, consumers will judge whether Algenist products are a breakthrough. In an unusual move, Sephora is introducing the line in 800 locations in 8 countries all at once, in a rollout coordinated with QVC. “It was a brand nobody has ever heard of,” said Allen Burke, the senior adviser for beauty strategy and development at QVC. “We want to give it a lot of visibility all at the same time.” But Mr. Burke knows that marketing has its limits. “It can be the most interesting story in the world,” he said. “But if it doesn’t deliver, it’s not a business that we can do.”