The build quality of this is very similar to the 24-70, in fact if the two are sitting side by side it is difficult to tell them apart at a glance. The front element moves within the lens barrel unlike to the 24-70 which has an element that extends outwards and like the 24-70 the there is no rotation so your polarizers remain polarized. The lens is constructed of mag alloy and polycarbonate and feels sturdy and well built, the one I had took some heavy knocks while I was travelling with no adverse effects. The rubber rings are well attached and very easy to use.
The SSM motor that Sony uses in these lenses is as quick as the other brands and at times it feels quicker than the Canon although that is subjective. It is smooth and quiet and on the A900 very accurate.
For a lens of this price you would expect it to perform optically, thankfully this is the case. Sharpness was uniformly good across all f stops and edge to edge as well even at f2.8. The tonal range on these CZ lenses is fabulous and combined with the superb edge sharpness gives it that CZ "3D" look, its hard to explain but the pictures say it all.
I had a CZ filter on the front which I suspect helped with any flare especially on the wide side of things. This lens is a worthy companion to the 24-70 and I suspect it slightly outperforms its longer brother on the sharpness front (bearing in mind that the 24-70 is one of the sharpest lenses around, this is no mean feat). If you have the deep pockets it will not disappoint.