It's a different feeling with the PJ. Pressure is applied to the top and bottom of the shaft and it can be very intense. You have to be carefull with it, because of the nerves and veins in the top of the shaft. Some have managed to use it sideways (rollers on the sides) but I found it very uncomfortable and not possible unless I hold from the glans with my other hand, to prevent twisting.
It doesn't replace manual jelquing IMO, but it is a good device to mix into your routine, and specially handy when you have no time for a full Penis Enlargement session.