Walimex rebrands Samyang optics and sells them in Switzerland at a reasonable price.
After a very good experience with the Samyang fisheye lens, I recently decided to try another one, disregarding some negative comments I found. Anyway there are not many serious reviews of this lens.
After creating an account, I selected "payment form shipped along the items" (which is common in Switzerland), I placed the order and I immediately got a confirmation message, so it looked like everything went smoothly; after about one week, nothing had happened, I wrote them an email and I was told that my shipping address was unverified (?), so they wouldn't ship.
I simply offered to pay the lens in advance (which they consider equivalent to a verified shipping address...) and I got the package in 2-3 days.
The box contains the lens, a bag and a T2 ring adapter, which you have to tweak with a tiny screwdriver. If you mount the lens as is, it may be arbitrarily rotated with respect to the camera body, so in particular the distance scale meter may point downward.
The lens is a manual reflex tele, it has a mirror inside, so it's very short and wide; it has a limited depth of field, and it's really difficult to take a picture in focus. With a tripod, and lots of patience, you can get some results; without a tripod, it's totally impossible.
However the lens is so cheap, that I consider it a welcome gadget anyway; it's not something that you will carry around for casual use.
Sony used to produce an autofocus 500mm F/8, which is still on sale even if I think it has been discontinued, but it costs 4 times as much as the Walimex.