The mixing ratios that are displayed on the bottle are designed to be mixed in a fuel can. However, if done carefully and the ratios are kept, Ethanol Shield can be mixed in the tank. For example, Preventive Maintenance requires 1 oz of Ethanol Shield. per 5 gallons of fuel. The fuel tank on your trimmer or lawnmower is much smaller so use a capful of Ethanol Shield to the tank.
Ethanol Shield will not hurt your engine in any way. In fact, Ethanol Shield will help keep the engine clean and allow it to run better and more efficiently.