The maker of the Peloton indoor bicycle is finally delivering its long-promised treadmill, the Peloton Tread. Over four weeks, we had 15 runners test the equipment as well as Peloton’s online classes. Our take: As fun as the Tread is to use and as good as its classes are, its high price—more than $4,000 at time of publication—and a weak warranty should give pause to all but the most fanatical Pelo-people.