For me this has been a god send as i need to play only 2 songs on slide in a set, and it fits perfectly on my little finger, therefore allowing me to play the rest of the chords quite freely throughout those parts when not sliding.
Im not a seasoned slide player, but this does just what i need and i personally found it better than a metal slide - or easier to control at least. I found it easier to pitch notes with the glass slide and as its quite weighty it seems to 'hold' steadier in one place than a lighter more skittish slide. It worked for me.