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You may be interested in this Slideshare by Wil Reynolds: http://www.slideshare.net/wilreynolds/the-10000-paid-content-paid-linking-test-that-is-100-google-safe Wil owns a large agency and tests out services like this including nRelate and Taboola. Some are better than others. As far as Google is concerned, as long as the links are "nofollowed" the recommendation services should be perfectly fine. In Wil's case, he used these services for link building, with mixed success. On the other hand, any content recommendation service that places followed, non-editorial links on the web is worth approaching with caution. I'm not familiar with the Engageya platform, but this is something I'd definitely check out first. Hope this helps! Best of luck with your content.