I think you're making a mistake by offering this for free. The kind of people who care enough about their web experience to install a new browser are the kind of people who won't mind parting with a few £$€ to do so. To be profitable, free apps must target the broader market, but this is a relatively niche product. I don't think you'll get enough IAP fast enough to be sustainable.
Why do you think Javelin is not suited for the broad market?
http://en.wikipedia.org/wiki/BrowserChoice.eu
http://en.wikipedia.org/wiki/Usage_share_of_web_browsers#His...