Carla from Compassion and Choices raised an excellent point in the comments of another post. End-of-Life planning is rarely straightforward, and it's important to fully understand all sides of an issue before you make important decisions.
There are some potential flaws in the simplicity of the Five Wishes format (a form I previously blogged about). Barbara Coombs Lee has written a nice piece about it. While its clever branding makes it memorable, and the positive framing of "wishes" is a nice language to cast death planning within, the form does have bent toward prolonging life that will not work for everyone.
The form does not allow doctors to withhold any treatment with the intent of taking your life. And it could be argued that many such behaviors than would be spelled out in a living will or advance directive could be cast as taking a life.
I'm a firm believer that any planning is better than no planning because, at the very least, you're giving your loved ones some indication of your wishes, fully understanding the implications of the forms you are working with is important to having the kind of death you would like.