I started using them when I bought my Rainsong, as a new set came with the guitar, (plus the ones on from the factory were unused.)

Since then, I have found them excellent on every guitar other than a Jim Harley dreadnought I use occasionally. For that, they are too bright. Also, as this is the only acoustic I use a plectrum on, I like a heavier string. Elixir seem to shine better on the lighter strings, or is it just me?

The longevity is one aspect, but I also find they squeak less when sliding up and down the frets. Some feel the squeak is part of the music, I don't. Hence I love them.

I buy quite a few strings and although they last a long time, I still get through a few sets a month all told and have found a supplier on Amazon seems to give best price / delivery.