One may ask - why bother with usual ultrazoom, especially not widely known?
Other question is - why AT-X (reserved for top Tokina lenses) mark on ultrazoom? Are they nuts?
I'll provide you some answers :-)
First. It is best ultrazoom, considering build quality. Solid aluminium barrel. A bit large, but feels perfect on camera. Second. This is parfocal ultrazoom, only one that I know of. It means that it maintains focus during zooming. Do you want to focus pricisely in 24mm? Zoom all the way in, focus and zoom back :-) This is main reason why it holds AT-X mark.
One of the downsides is very short focus throw and small focus ring. One of pluses - normal and handy aperture ring.