i drive a classic mini, and as such frequently find myself in trouble with flat batteries, usually due to one of many poor alternators. i bought this from amazon and have used it well over a dozen times, as much as 4 times in one day and it always performed instantly.
i would gladly pay far more for such a useful tool considering how many times it has got me out of hot water, including breaking down in the middle of a main road. simply hopped out, plugged it in and off i went. as quick as that!
the other reviewers views on this tool are simply wrong, i can only say he must have not charged it the recommended amount before first using it. All batteries are 12 volts so there is no way it could not work on ANY car.