It compensates for the poor signal given by the OEM MAF sensor. Mate of mine ran one and it made a big difference, it was on a diesel MG and it ran great after a few test drives and tweaking of the dial (which basically just amplifies the signal from the MAF and then gives that to the ECU). Either play with the dial and tweak it till it runs nice or get a new MAF and remove the amp thing. After a while your new MAF will probably start to die though, hense the amp thing was invented!