I am a choir director and I bought these books because my priest recommended it. Physically, Hieratikon Vol. II (Divine Liturgy) is a durable little book with very nice, sturdy binding, a solid and aesthetically pleasing cover, and handy ribbon bookmarks in the bindings to mark off important pages. It is well made and well laid out. The texts are black and red, indicating what is being said and what is being done.
Obviously, Priests and Deacons need both Vol. I and II in order to serve the services. But for me as a choir director and the primary person who puts together service variables into binders and packets for the choir fir my parish, having my own copies of the Hieratikon Vol. I and Vol. II has been extraordinarily helpful to have as reference, and also to follow during the services - particularly during the services that are less frequently served. It helps me to put the music and cues, as well as the reader portions, into an organized and coherent whole so that the choir and Readers can use our binders to follow along with the services while not actively singing/reading. In addition, knowing how long the priest needs for various prayers he is saying quietly (for example, during the Anaphora) helps me to time the singers' tempo properly, so that the clergy aren't waiting for us, and we're not waiting for them. I recommend all choir directors, both new and experienced, have a copy of the Hieratikon on hand.
This final note is not a complaint at all but an observation: if you have trouble with small print, consider buying the large Altar-size version of these volumes. In order to fit everything into a smaller book like this, the font used is also on the smaller side.