I'd even go as far as saying it's barely usable at all.
You can't tell anything from it at a glance; you have to hover each "ray" one by one to know what it's about, and then most probably for at least the first 5 or 6 times look at the top left to know what browser each color represent; and you're supposed to know what each feature presented actually mean.
really? can't the same be said about any language with graphics support? it's not a consumer-facing product; it's a language. it's what you make of it.
The intention of this visualization was to show how much support exists for a particular HTML5/CSS3 feature among the 8 browsers, but not which specific browser supports which feature, which are already covered well here: http://whencaniuse.com