I like that it allows me as an SEO expert or even someone who is just interested in website speed, can test their own sites for loading times of pages with different content sizes (images included).
It's easy enough so anyone could use this web tool without needing any training! There really isn't anything i dislike about geek flare other than perhaps there would be more options available if you have larger websites/pages. If nothing else its still useful when testing smaller sized areas within my client projects' home page designs - especially since they are often too busy building up images etc which slow down loads further once those elements come into play :).