In space and equipment: a shower pour uses the shower you already have and a container for your strained preparation, while a foot soak needs only a basin of warm water set anywhere you can sit comfortably. The foot soak is the more private and portable of the two; the shower pour covers more of the body.
In preparation and timing: both follow the book's consistent recipe format, but the book includes a foot soak you prepare the previous evening, so the practice itself takes only minutes the next day. A shower pour fits into a shower you were taking anyway.
In focus: the peppermint foot soak, for example, narrows attention to everyday sights, sounds, and sensations, then asks you to choose a small task. A shower pour keeps the full upward or downward pouring symbolism of the bath tradition, which a foot soak expresses more quietly.