One paddle can be quite sufficient in a smaller drum. The point of the paddle is to provide enough added friction to cause the load to roll. Large paddles in a small container can produce the paradoxical result that the load moves as a static whole, with no (or less) relative motion or mixing action. Also in a narrow drum you can get decent rollover and mixing action with no paddles, depending on friction between the load and the surface of the drum.
The placement of the plastic paddle opposite the door, seems intended to counterbalance the added weight of the hinges and latch on the door.
Horizontal-axis TLs by definition have "invisible" washing action (you can't watch). The closest you're going to get to being able to observe the cycle is by fitting a clear perspex lid over the top and bypassing the safety switch on the existing lid. (You need a lid otherwise the spin cycle will help wash your ceiling as well as your clothes!)
The closest we're going to get to visible washing action is if e.g. Staber made a unit with clear front panels on the inner and outer tubs, and a clear front cover. This could be done, and if the rear panels on the inner & outer tubs were also clear, it could include a light behind the rear of the outer tub, which would shine all the way through.
As far as the relative efficiency of Staber vs. others, the drum geometry could be equally efficient if a lower overall water level was used, counting on the "pumping" action of the drum geometry to compensate for the added clearance space. Probably the majority of the Stabers are sold to buyers in remote areas who prefer the simple & robust construction and the ability to easily self-maintain the machine over the years. Simple DIY maintenance is a compelling sales case in a rural environment. Many buyers are off-grid using solar and/or wind power (some for ecological reasons, but many for the simple practical reason that it would cost them more to extend grid power to their locations than to install their own solar & wind equipment), and have wells for water, so maximum electrical efficiency would be more important than maximum water efficiency.