If it really is sodium cyanide, it's deadly. A small amount (less than 1 gram) will kill you in a few minutes. Death is not particularly pleasant, judging from what I have read about the symptoms of cyanide poisning, but I don't think it's exceptionally unpleasant either, and anyway it's all over very quickly. But if it's readily available I would have to wonder whether it really is sodium cyanide. Note that if not stored it a sealed container, it will gradually release hydrogen cyanide, and what remains would then no longer be toxic. You should read carefully what it says on the label. It is is real, and if you do use it, please be careful not to leave any lying around where it could harm other people.