I got this to start learning slide and compliment my glass slide. Also because it will instantly enable you to play like Joey Landreth (please contact TRS or your chosen god with any complaints).
Pros:
The inner is bevelled so that it fits on the pinkie perfectly.
It has a cutaway at the bottom to enable the free movement of the knuckle
It has a groove cut into the side of the metal to enable the ring finger to sit snug and hold in place
It's a great size.
Cons
Not really a con, more a preference - it's heavy! If you're looking for a light slide, get a glass or maybe ceramic one. this is a nice chunky piece of brass.
I've just started with this, but so far it fits beautifully and is inspiring me. It is for the PINKY finger. This is important. If you play slide on another finger this may not work for you. Also while it fits perfectly on my pinky, if your hands are very large or small that may not be the case for you.