I have and use the first version of the Tokina 12-24, which based upon the sale price is probably what you are looking at. It's a good lens... better built than the Canon, nearly equal IQ, just not quite as wide and the Canon is exceptionally good handling flare, while the Tokina is merely "very good" handling it. The 11-16/2.8 might be a wee bit sharper, but is quite prone to flare and costs more.
Don't worry about the original version or the version II of the 12-24 on your Canon camera. There is very little difference between them. Supposedly internal coatings were changed in some way. There is a much bigger difference in the Nikon mount version, the II has an AF motor added so it will focus on all Nikon cameras. I think Tokina simply updated the lens in all mounts, at the same time.
The price is good for this lens (at least it would be here in the US)... not a steal, but not overpriced either.
The lens can be fun to work with, I find 12mm wide enough and f4 plenty fast.
I deliberately made the following image the worst possible way, to push the lens to its limits. Normally, shooting into the sun and glare like this, I'd have used a full frame camera, prime lens (20mm) at a middle stop and avoided using any filter. Instead I made a point of using the 12-24 on a 7D with a B+W MRC C-Pol on it, and underexposed... I was pleasantly surprised how well the image came out, though it's not perfect and some post-processing was needed.

Late afternoon, Pigeon Point..
Tokina 12-24mm f4 lens at 15mm, f10. EOS 7D camera at ISO 200 and 1/640 shutter speed. Handheld, avail. light. Here's the image more straight from the camera...
As you can see, its underexposed, there are some "ghost" flare artifacts (fewer than I expected, and more easily fixed), overall veiling flare causing loss of color and contrast. There is also some chromatic aberration, though you have to zoom way in and look for it, mostly toward the edges. Here are a couple details showing some of the flaws...
These are far less than I expected and the image was much more easily recovered and retouched in Photoshop than I thought it would be. I credit a lot of that to the 12-24/4. Othe UWA lenses I've tried wouldn't have fared as well.
So, I'd encourage getting the lens and giving it a try. Buying used, if it's not from a store that offers a warranty, be sure to check out the lens as thoroughly as possible.