I used to just use a dot, as about all I was interested in was where the bullet stream was going and really didn't like clutter.
I read several of Bustr's posts about the 100 mil rings, and it started me thinking about stuff. I downloaded his pack and have found them to be a huge asset on .50 equipped planes in particular. It gives a pretty decent indicator for approximate lead on certain shots that crop up often enough.
The historical aspect of them is a nice side bonus.
I'd put it somewhere along the lines of wishing for 1, 2, 4, 5 for me.
Wiley.