Do you not find the output to be a little uneven around the ring? I'm tempted to get one just to add catch lighting.
Yes and no. Yes there is a gap at the top of the flash where there are no LED's and therefore no light and so yes you can get some fall off at this point. If shooting portraits then if you far enough away to use a 90mm lens (zoomed in to head & shoulders composition) than you can get flash fall off all around the edge of the subject because the flash doesnt throw a wide 'beam' of light but focuses it into the center. However at a zoom of 70mm or less it's pretty much fine and for close up stuff it's perfect. Ultimately though you have to factor in the price and adjust your expectations to match. Is it as good as a dedicated ring flash? Not really, at least not in all situations (although in some it gives it a serious run for it's money), but a dedicated ring flash is going to cost at least £300. This costs £25!
I bought it mostly for doing close up work with the occasional portrait and for this, I think, it's great considering it's price. If portraits are more your thing then, if you have the money, get yourself a dedicated ring flash. If you have studio lights then you should be able, with a flash meter, to be set the ring flash to give you nice catch lights and the studio lights to compensate for any fall off. That said when I used to have studio lights I used to get nice catch lights just by using softboxes but clearly these aren't as portable as a ring flash!