The various ones that I have seen show various constrictions from cylinder all the way to extra full, all you would have to do is stop the adjustment inbetween the imp cyl and mod to have light mod, or to find the best choke/load/pattern combo, much the same way that the Browning BOSS system allows one to find the sweet spot for a rifle. There is also a new kid on the block by Tru-Glo called the Titan adj choke tube.
http://www.truglo.com/products/choke_tubes/
From the Technoid: The patterns from the Poly-Choke were good too. I could go from a true cylinder bore to a tight Modified. You do have to do some experimenting to find out what point on the dial gives you what pattern, but that's not too onerous for a true Junior Technoid.
http://www.shotgunreport.com/TechTech/T ... ug-02.html
and from the poly choke/marblesoutdoors site:
Poly-Choke® settings include:
•X-Full (Close)
•Full
•Improved Modified
•Modified
•Improved Cylinder
•Slug
•X-Full (Open-Cylinder bore)
•Two Settings Past Cylinder Bore
http://www.marblesoutdoors.com/polychoke/index.html
as to diffussion, this is rifling that can be either straight or tradtionally helix, that is designed to even a patterns spread. If you are asking about turning the diffussion off, I suppose if it were made as a seperate threaded portion that could be removed or just leave it in to act as a jug choke.