Worth a guinea a box.

The phrase "Worth a guinea a box" is an idiomatic way of saying something is extremely valuable or effective—so good that each small unit (a “box”) would be worth a guinea (a high-value gold coin in Britain). It often implies a product—commonly a medicine, ointment, or luxury consumable—whose benefits are considered exceptional relative to its size or cost. As an anonymous, slogan-like line, it reads like advertising copy or a stock commendation rather than a literary aphorism, emphasizing perceived value through a vivid, old-currency comparison.