The focusing range is naturally very small, so you need good results for a little practice. But if you have the hang times, one has the intent really a good addition for macro photography. I do not photograph this way, with the autofocus, but manually by slight movements back and forth.
I use the Raynox DCR-250 intent eg in combination with a Canon 100mm macro lens. This combination provides the use on my Canon EOS 500D good results. However, here is the focus range is extremely small. Here I have achieved in comparison better results with the DCR-150 intent. So I use this intent rather then with other lenses. Problems with vignetting on the edge or in the corners I have not found.
The handling and attachment to the lens are very simple, I do take part in a small purse.
For a truly useful accessories at a very fair price, there is of me 5 star and a strong buy recommendation.