Spellbook isn’t for everyone, since it’s sort of an unusual approach to sequencing, but the Index input does give you two different styles of CV control for addressing specific steps, and Spellbook can handle sequences of any arbitrary length, which sets it apart from most sequencers.
As an alternative to clocking/stepping it, the “Index” input can accept either a “Relative” CV control of 0v-10v to move through the sequence proportionally, or an “Absolute” CV control specifying a specific step using an integer voltage.