What the papers said:

Using little or no vibrato, the group conjures a smooth, unblemished timbre like alabaster rendered in sound. Singers are hand-picked to create an aural pyramid, with light, high voices - enriched by, as far as one could tell, three male altos - resting on a sturdy bedrock of basses. Far from compressing the timbre, such careful structuring allows rare lucidity and resonance.
THE EVENING STANDARD