I think this tool has more value in attracting advertisers, than in actually selling your site, they can see the number of visitors, how old and therefore how high up in searches your site is, how many outside links lead to your page, etc..... The more your site is worth the more worthwhile it would be to advertise there...
Maybe I should contact these folks and drop in an idea or 2 like looking at the amount of free space on the site as available virtual real estate for ads and calculate potential worth of that in a separate column....