The first thing to know about this set is that roughly three-quarters of the tracks are recordings made in the early 80's, when the Cocteau Twins sound was heavier and darker. Stronger rhythms and more droning guitars than what you might be familiar with from their later works. If you liked Garlands or other releases from that era, you'll love this.
The remaining tracks are mostly from Milk and Kisses. On these tracks, especially, it's easier to hear details and nuances of Fraser's vocals that get lost in the highly produced studio versions of the tracks. This is especially noticeable in the quiet and personal "Half-gifts" and some of the heartier signing in "Seekers Who Are Lovers".
My only quibble with the album is that it's questionable just how "live" some of these performances are, particularly the recordings from the 80's. In spots, Fraser is obviously singing along with tapes of back-up vocals (either that or she brought a clone into the studio). Nearly the first minute of "The Tinderbox (of a heart)" sounds identical to the studio version.
In contrast, the tracks from the 90's sound more "live" (either the drum machines are better, or there are real musicians sitting in), and Fraser doesn't use any taped backing vocals. Since there's a lot of multi-tracked vocals on these tunes, Fraser has to choose which parts to sing. Although this helps you hear her singing more clearly, the absence of some of these parts leaves the songs sounding incomplete (especially true of "Violaine").
Still, those minor complaints aside, this is a great listen. Fraser's unique vocal style is why most of us love the Cocteau Twins, and it's great to be able to hear it front and center over the long evolution of the group's sound.