Some new dryers tumble both ways and a lot are now single direction......
You might be inclined to think that reverse tumbling is essential as it is designed to keep the clothes tangle free.
The reasons that dryers of a single direction action work well, is the design of the drums the clothes tumble in.
One make has a protrusion in the back of the drum. It is nicknamed a Pinocchio, as it sticks out like his nose. The presence of this 'device' is reported to assist in keeping the load free. Some Bi directional dryer drums do not have paddles, as a general observation. New single direction models have paddles to lift and drop the load, so loosening the garments to prevent balling. Also the shape of the paddles is significant. They are not straight lined but are somewhat curved in two directions.
If you are purchasing a new dryer, ask the salesperson about this. A salesperson sufficiently 'schooled up' about the product should be able to advise you about these intricacies. Then you can choose a product that you will understand and feel comfortable with....Ask Tony