We are using 20mm diameter by 10mm thick neodymium magnets, with a pulling power of about 6 kg or 13.5 pounds each. The mounting system is simple and basic - it's a plate of steel. It's not pretty, and you will notice that the bottom of the magnet is exposed. This is on purpose. It increases the available amount of magnetic force directly transmitted to the object that you want to have an effect on. If we were to cover it with a layer of plastic, as is the usual procedure, we would reduce effectiveness by somewhere around 20%. The magnets hold on to the steel strip with a pulling power in combination of 27 pounds. Their polarity can be changed, and they can be moved around; we sell it with opposite poles up, because we have found in tests that the best fuel efficiency increases occur when fuel passes through opposing magnetic poles in succession, on a horizontal plane rather than on opposite sides - just as we have them here. The fact that there are two magnets also offers an interaction between the poles that would not be present if there were only one magnet with opposing poles on the same side.
And the price? Its $29.50. This is inexpensive for this kind of application. The cases of the competition are prettier, and the prices sometimes double, or more - in any case, significantly more expensive, with no added effectiveness. This is probably the cheapest, but most effective for the price, magnetic fuel enhancement that you will find available for sale on the internet anywhere.