For two and a half years I have tried very many self-propelled treadmills and can say that they are not all the same. Some of the self-propelled treadmills are very bad but others are decent. Talking only about the decent ones , they all have the same issue ; they are excellent for running or jogging but not that great for walking slowly , let me explain ; When a user wants to walk slowly , the belt , as it sits on top of many bearings , it will tend to jerk a bit depending on your body weight , and , when walking slow , is very difficult to control and have constant speed , but , if you add magnetic resistance , that will change things for every user. My conclusion on the subject is that is vital to have resistance in a self-propelled treadmill to make it more comfortable for users that want to walk slowly. Resistance will also enable users to use the self-propelled treadmill as a SLED in Crossfit studios.