What makes them attractive is that they are easy to install and they don't cost too much so when paired with a budget-priced router, you can build a tandem system that gets as-good or possible better coverage than what you'd get from a single high-priced router. Range extenders come in various shapes, sizes, and speeds, but they have their limitations; they are typically half as fast as your primary router, and they create a separate extended network that makes seamless roaming difficult.