Ok, so a set of £13 lenses are never going to give you top-notch quality... or are they??
I have taken dozens of shots with these lenses and so far the results have been very good(using a Nikon D3100)
Indeed, the end results surpass photos that I have taken with other cameras.
A few tips from this novice, to the other novices out there:
Yes, you can use more than one lens at a time, but the in-focus field of vision will get narrower with each additional lens you add - magnification of just 1x or 2x, is more than enough for close-up work... any more than that and you start to narrow the focus too much.
You may get some minor 'fish-eye' distortion around the edges (depending on how much magnification you are trying), but it doesn't really show on the photos I have taken.. it is more noticeable when you look through the viewfinder and move the camera around.
If you are using the 18-55mm lens, you can still zoom in/out as you would with any other shot.
For what they are and for the price you pay, I think these are a very good (re: cheap) way to take macro shots.
I have posted images on Flickr and have had some very good feedback on the quality of them.
I can understand some people might prefer a proper macro lens, but if like me, you are on a tight budget and the thought of shelling out for a pricey macro lens, leaves you cold, then give these a try..
for £13 or so, you can always chuck them if you think otherwise.
PS.. I will try to upload an image taken with one of these lenses, so that you can judge for yourselves.