They work fine - if it suits what you want to take shots of then fanny's your uncle :) I used one on the shot I just posted into Tom's thread about photographing small objects. They usually require you to focus manually. I use the Canon 250D close up lens.

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html