Has anyone tested these yet? MXA magazine tried it and liked it enough to give it 5 stars for a yz250f. According to MXA, this is an air boot with 2 different velocity stacks to choose from, a short and a long. Their test riders all stated they felt a noticeable difference from stock and between the 2 choices. The dyno backed this up with a 1 hp gain. A 1 hp gain from a bolt on is worth looking into.