Why is Sequoia Looking Into Associative Browsing Add-on SimilarWeb?

Yahoo's purchase of FoxyTunes for a rumored $30M legitimized the add-on play as a product strategy for Israeli startups. I see new startups in this category almost weekly. We're bearish on add-on plays because the “get them to download, install and use” parts are tricky - and monetizing those users is nearly impossible. In recent months, though, SimilarWeb's name keeps popping-up and the reason may be the technology it's spent two years building out. Sequoia Capital Israel, we've heard, is spending extra time looking into it and your typical add-on play doesn't normally make their cut. So what is it about this little company?