Extended contact lenses are easy to cause eye infections. However, this kind of contacts is designed specifically for overnight use and long-time use because they are more permeable, which can allow plenty of oxygen to get into the eye. As long as you use them in a right way, it is safe to wear extended contact lenses. If you get any eye problem, you should go to your doctor as soon as possible.
Pesonally speaking, I would not suggest to wear contacts cuz they have a higher risk of getting infection than wearing glasses. Though extended contacts are designed specifically for overnight use and are also far more permeable, you can also get irritation and other eye problem when using them.