in theory they do make a difference, although nhow noticeable it actually is is up for debate i guess.
The splitter makes the front end about 2cm closer to the ground, so restricts a fair amount of air from going under the car when urdriving, this creates an area of low pressure under the front wheels which helps keep the front end a tad more planted.
Not that you'd dver notice, they do looks good tho, hehe.
lewis.