From my experience, it is VERY effective... It allows an instant adaptation to circumstances from one single initial movement.
What PV explains is that ikkyo to yonkyo are evenly distibuted on a downward spiral. When you rotate all techniques fall quite naturally from ikkyo, minimal rotation to yonkyo max rotation. The simplicity of the priciple behind is quite stunning, one entry, one rotation, many possibilities according to circumstances.
The kajo series
may be of a great help to undesrtand the logic behind these related movement as explained in "Budo".
I can only but invite you to read them with an open mind, after all it's free knowledge and you can make honey out of it if you feel it is of some value, otherwise, discard it.
As for redirecting you to TAI website, it is only a matter of convenience, of course you will do as you like
To have a real discussion on the forum it is not enough to write "yes it is really effective" -- as we don't have any common definition what ‘efficiency' in aikido is LOL And!! even in the same dojo, what is efficient for a beginner may not be efficient for more advanced student.
Instead, please read my post carefully, I wrote few arguments from biomechanical point of view. Could you please address these arguments?