Hi Ray,

I don't know if they are "universally" accepted, but accepted well enough.

Personally, I don't think I'd use a furled leader without one. It just makes life easier for me.
I don't think there's any problem using them on mono leaders.
You can use them while dry fly fishing. Smaller is generally better. I just apply floatant to the ring itself, the leader above the ring, and a few inches below the ring. That will help keep the ring from trying to sink.

One thing that I really like about them is that you can change tippet sizes easily without having to step down the leader with various sizes if you are making a large change in tippet diameters.

...just my opinions.

Brian