The slower brother of this Sigma seems to be a tad better lens but it depends on your shooting distance. If you can find a properly centered 4-5.6 version of this lens or Tokina 11-16 mm lens, you should be fine even with corners after stopping down.
All these lenses have QC issues (including Tokina) so it is worth comparing a few before finalising the sale. For example, I have now tested a couple of Sigmas and three Tokina 11-16mm lenses. The differences are no minor if you do critical work. So a good copy of this lens can beat a bad copy of Tokina - which explains that mixed reviews which can be found from the net.
I have been using this for a couple of weeks. Appears to be quite accurate, needs 1-2 minutes to stabilise but after that pretty much spot on. Not the most logical menus but for this price I am not complaining!