I have the Samyang (Rokinon) 14mm on 6D. This is a great lens, with excellent sharpness and very low price. However, you have to keep in mind that 14mm on FF is VERY wide! I am very happy to have it and I have never regretted buying it, but I can't say it's my most used lens since it is often just too wide. It really depends on how wide you want to go; the 16-28mm FOV is much more practical, but the 14mm is much more unique!
Also, do you have other wide angle lens? For instance, if you already have a 24mm, I would recommend more easily the 14mm than if your widest lens is a 50mm!