I am yearning for this lens to use on my upcoming trip to China. The f/2.8 aperture would make it an excellent low light glass.
However, I have and I absolutely love the 12-24mm f/4 Tokina and, in the interest of saving money for my trip, I am going to bite the bullet and stay with the f/4.
Since you are new to UWA lenses, let me share a few things with you which you may or may not be aware of...
1. When shooting landscapes with the UWA, I have found that including a really prominent foreground object such as a rock or a plant of some type really enhances the image by providing a sense of proportion and leading the viewers eye into the image
2. When shooting a full body shot of a person, shooting from a bit lower angle will reduce the distortion which makes the top of the person's body look much larger than the legs and feet. Shooting from eye level causes the distortion since the top of the body is much closer than the lower portion.
3. UWA lenses are very sensitive to the camera looking up or down and will produce distortion. Having the sensor close to perpendicular to the ground or floor reduces the tendency to distort.
I hope that you are not offended by these simplistic hints. If you are already aware of them. please excuse me.