In Europe (f.e. germany) they're called "Walimex"
The quality should be all the same because I think they were mady in exactly the same factory.
I *love* mine, especially for the price. The resolution is terrifice f.e. @f8 and it's not that big or heavy. The only thing I have to mention is a general one... don't use those lenses (just) for landscapes. Wideangle lenses in this range are not made for panoramic pictures, at least not in my opinion. Just use 24mm with straight optical lines and stitch a few together if you need more angle of view.
The Pixels on the border are curved, unsharp and the results may not be what you've expected. With film you have to, but with digitalcameras I would stitch. Wideangle lenses @14mm can be much more usefull for creative purpose, to catch the eyewithin rooms or to shoot in rather tight places.