OP3 is a great tool and a great idea, but unfortunately the reason most existing prefixes have so much market share is because they are tied in to advertising. Podtrac is the biggest player despite being a crummy analytics tool because podcasters use their Podtrac ranking to signal their reach to advertisers. Everyone uses Podtrac so the numbers are apples to apples. I sincerely hope OP3 gets enough critical mass that it can fill the same need.