Advantages

They can be made anywhere in the World where people can weld, do woodwork, etc.

They can be used in rivers or streams.

They can be mounted on bridges, or on their own support gantry.

They don’t need any dams or leats, pipes, etc.  Just a flowing river or stream.

They don’t interfere with fish, because they can swim past in either direction, and if caught in the rotor, they just come out unharmed.

They can be installed in millions of suitable places in the World.

They can supply a local need for electricity, or be connected to the electricity grid.

This is also the scale that allows electricity to be fed back into the grid by using the same cables that brings the electricity out to people!  No new transmission cables needed!

The concept is Open Source: there are no patents: anyone can build one, and improve it, if they want.
(Note: the Carruthers type is patented.)

They could be mass-produced if required.

The diameter and the width of the rotor can be designed to ensure optimum electricity generation for a particular site.  For example, the Hydrotor (waterwheel) could be made a much smaller diameter – and increased width, if possible – to rotate faster to suit the generator.

The generator can be fitted externally, for ease of maintenance, or swapping for a different size or type of generator.  It is probably the costliest item in the design which will have to be purchased.

The design of the unit, with an adjustable balance weight and variable Height Adjustment Float, ensures optimum electricity generation at any flow of the water, automatically.

They could be made using second-hand parts, e.g., generators from scrapped hybrid cars, old waterwheels, etc.

There could be an array of several units strung across a wide river, or there could be several, one after another in suitable places in a stream.

Small is beautiful! Could help Zero Carbon Britain – “Powering Up”.  But powering up The World!