Yes, I have used the 17-40L and I don't particularly like it. The first reason is on a crop it's not an UWA and it basically becomes, at best, half of a general zoom. I reasoned that I was better off with an UWA made for the format because it's a more appropriate application and a proper general zoom, the 24-70. I also wasn't blown away by it, there are many people who get great results out of it, I can not.
As for the Tokina on fullframe, yes, it only does work in the long end of its very short range. Not such a big deal as it's more of an adjustment from 11 to 16 than it is a zoom
. I wouldn't recommend it as a lens to shoot landscape on full frame though, get a UWA made for full frame if that's your plan. The 16-35L, 14L, 17TS, 21mm Zeiss... and Tokina is coming out with a 16-28
for full frame if, like me, you don't like the 17-40 there are lots of options.
On UWA is the only time the crop factor is a pain. Every other instance I like the extra reach just fine. Easily solved with the very competent Tokina which you can sell quite easily if you make the mad dash to full frame glory.