I would love a treadmill, no room unfortunately.
It is an excellent tool for fitness and rehabilitation.
It is not designed to replace hiking, road walking, swimming or any other type of exercise but can be very useful for a number of reasons.
there are people who work full time, and in the winter for example available light is at a minimum.
so the dog can be exercised on the treadmill during darkness and then the time available can be used for training in whatever discipline.
there are also people who live in very rough areas with lots of glass around, this avoids any accidents.
It is a tool which can be very useful.