A niche lens, but one that should be considered if you shoot on a Canon or Nikon APS-C DSLR and require a wide-angle zoom with a fast aperture at a reasonable price.
Fast maximum aperture; Construction is more robust than many budget wide-angle zooms; Practical size without being too bulky; Affordable
Doesn't allow manual intervention in AF mode; Noisy AF motor; Doesn't always engage fully into manual focus mode; No weather sealing