If it's the full-size text book that I'm thinking of, it's largely a waste. You don't need to devote a full textbook to piston multi operations. Other than single-engine aerodynamic theory, most of what you need to know is airplane-specific: manuever procedures, fuel-system, prop governor and feathering systems.
I wouldn't spend the coin unless your training program requires it. I had to buy it when I got an MEI job, thumbed through it once, and never opened it again.