This is a very interesting accessory... if it works with a 430exII then it will get added to my kit, thanks for the tip and nice bird portrait!
Yes, they have a model for the 430EX II - the FX5.
You'll be better off with a more powerful flash in some cases (I have one for my 600EX II), but the 430 will work. What's more important than flash power is getting the flash off camera - you'll want a flash bracket with an off-camera cord to get the light off the lens axis and reduce 'steel eye' (the avian equivalent of red eye).
Also, take the fresnel lens off when not using it - it works both ways, and the sun shining down on your better beamer turns it into a better burner (fresnel lenses are used in solar backpacking ovens), and you can melt your camera gear or your skin, depending on the angle of the sun.