I bought the 14mm after reading the hype and it was awful. Users also said it was EF, but it came with a note in the instructions stating that it was optimized for crop cameras and FF users should expect poorer quality. That was a understatement.
Hmm, that's strange. All the things I've read, as well as reports from a couple friends who recently bought the 14mm for FF cameras, have all said the IQ is excellent, particularly in the corners. From what I've seen, corner performance on the Samyang 14mm is vastly superior to any WA/UWA Canon Zoom, and still better than canon UWA primes. The only major issue I've heard of for the Samyang 14mm is the barrel distortion, which is apparently pretty bad. Not sure that is an issue most of the time for landscapes and astrophotography, though (which, aside from architecture, would be the lenses primary use cases.)