Well - The SLRMagic 12mm is nice. But the problem is the quality and quality control. There are alot of lenses out there with HUGE amount of dust or paint "particles" inside the lens system (which is normal according the support). And many SLRMagic lenses also had play inside the mechanics. Don´t get me wrong - Maybe the mechanical problems are solved already - But the dust particle problem was a few weeks ago -.- So from my side SLRMagic is a "no go".

The Tokina 11-16mm F2.8 is nice. But you always need an aperture control ring feature on the adapter. Not THAT of a problem though. Cheap ones are priced around 20 bucks. But in general maybe a RJ Lens Turbo + a Tokina 17mm F3.5 lens (with nikon mount for example) is for sure the better choice. You get a ~12mm F2.5 lens (with the 17mm on the focal reducer). So not the fastest speed (aperture wise). But a quite nice lens (and you get everything for about 200 to 300 bucks (so the half or a THIRD of the SLRMagic 12mm). And you can also use other lenses on the focal reducer. 24mm, 35mm or 50mm lenses (gives you 17mm, 25mm and 35mm focal lengths with 1 stop faster aperture on the RJ Lens Turbo for example).

Btw.: Also the Rokinon / Samyang 16mm F2.0 is usable on the focal reducer. Gives you nearly 11mm with F1.4 (!) with the focal reducer. So even faster than the SLRMagic. And you can also use all lenses with a normal adapter. So you also can use it as the standard 16mm F2.0 lens. ^^

LG