Clickworker is very different to Textbroker. For starters it seems to be run by a German company and when you google the website, the subtitle that comes after the title is human grid. Think about that for a second. A human grid, that's us, the writers. Writers in a great big grid writing tiny articles for corporations.
It's not as bad as it sounds actually. It is, once again, an SEO content provider. Clickworker essentially mediates between the big boys like Groupon and the little guys like us.