This collection contains; God Rest Ye Merry Gentlemen, The First Noel, See Amid The Winter's Snow, The Wassail Swing (Here We Come A Wassailing), O Come O Come Emmanuel, Carol Of The Bells, and I Saw Three Ships.
The trios vary in difficulty level so some are pretty much sight readable (or can at least achieve pleasing results with minimal practice), others, such as I Saw Three Ships, provide more challenge (it's in mostly 7/8 time and at a lively tempo).
The parts are written as to appeal to mixed ability players; the lower part (Flute 3) is generally the easiest and largely stays around grade 3-4 or under. The middle part (Flute 2) is about grade 4-5 maximum level in pitch range, but generally has more notes than the tenor part. Flute 1 receives far more of the technical gymnastics but still, around grade 6 is it's maximum difficulty level.