Benefit: You can use a blade boot as an off-hand weapon.
Action: Releasing the knife is a swift action; rearming it is a full-round action.
Drawback: When the blade is extended, you treat normal terrain as difficult and difficult terrain as impassable.
Pathfinder Companion: Adventurer’s Armory. Copyright 2010, Paizo Publishing, LLC; Authors: Jonathan Keith, Hal Maclean, Jeff Quick, Christopher Self, JD Wiker, and Keri Wiker.