It should be obvious that an oscillating drive roller (replicating hand rolling) is a preferable and more efficient way to felt than one-way rotation.
Imagine if you will an agitating top load washing machine. When you put your garments in it and it agitates backwards and forwards you intuitively and correctly, expect that it is this agitation that cleans the garments. If your top load washing machine only rotated the dirty clothes in one direction you would not expect that it would be very efficient.
The same is true for felting. Agitating the fibres against each other with a forward and backward motion is preferable to a simple one-way rolling motion, which pushes the fibres consistently in one direction.
The only time that we would recommend one-way rotation is at the beginning of a very large, heavy or tricky piece of work where your goal was simply to “bed in” the materials and create an initial contact. After a short cycle of one-way rotation, and with the materials secure, you would return to the oscillating (forward and backward) motion which is much more efficient at generating felt.
(The oscillating motion is patented and only available on The Gentle Roller)