How Useful Is a No Electricity Treadmill for Home Workouts?

Last Thursday I visited a friend who had set up a small workout corner at home. Instead of a regular treadmill he had a no electricity treadmill which works manually. It looked simple but I started thinking if it is really useful for workouts or just a basic alternative.

Watching him use it made me think about effort and control. I realized that manual machines may offer more control but also require more energy which made me curious about long term use.

Later I checked online for more options. While casually scrolling online marketplaces including alibaba I found many manual treadmills in different designs and price ranges. Some looked sturdy while others seemed very basic.

Now I am thinking if a no electricity treadmill is actually effective for fitness or mainly a low cost option. Has anyone used it regularly and seen good results?