I've had mine for two years. No negatives - power steering, water pump, and A/C work exactly as they always did. Power increase is only noticeable (to me) on the track so as Porsche9 said, its there but you barely feel it or get used to it very quickly. Worth it? Yes, +5hp is always welcome for such a low cost. Wish I could find 20 more things that cost so little, have no drawbacks, yet yield +5hp each.