What is the relevance of iba opt out by google?

Those extensions and similar ones do exactly what it claims to do (and they are open source): reduce targeted ads from companies tracking you online and as you concerned about the privacy issues, the IBA Opt out by google extension you linked to for example states: Stops interest-based ads on some of the websites that partner with Google In the Protect My Choices extension you linked to, Google Overview statement says: Protect My Choices applies to interest-based advertising by participating companies. Once you install this extension, you will still receive online advertising from participating companies, and the Web sites you visit may still collect information for other purposes This means those Google partners (companies) still pay to have their ads displayed there for users so there will still be targeted ads in areas outside Google's control. So you can see your privacy is the last concern of Google which is rather making everything to keep advertisers happy.