It comes in two parts. There is a 2.5x (focusing at about 4 cm) close-up lens at the back and the convex wide-angle converter at the front. You have to use both parts screwed together to get the wide angle conversion.
With this lens, my 28 mm Tokina lens gives me the effect of a 21 mm wide angle lens, which is a very nice wide angle since I also have a Nikkor 10.5 mm fisheye. With my combination I have 10.5mm (which gives me the DX equivalent of 15 mm), a DX equivalent of 21mm, and a DX equivalent of 42 mm. Edge to edge sharpness isn't the greatest, but I work around it.