Outer ring - who uses and what are your findings

That is why I use one and it works.

It works.  Have made it part of my "ritual."

Thought about buying one for my Prime but it would just be one more thing for me to obsess about. 

I have one for my Kenwood L07D.  I don't routinely use it, but when I did use it, I placed it directly on the platter edge, UNDER the lip of the LP, so that I didn't have to remove the ring every time I played another LP, with the attendant risk to the stylus. 98% of the LPs that I keep and play routinely are already flat; for me the ring is only to add peripheral mass to the platter to increase inertia.  (I'm not saying it wouldn't work to flatten a warped LP and perhaps to dampen resonances; I'm just saying that it's an aggravation and a risk to use it that way, and I don't feel I need it for that purpose.)