The feet per minute (FPM) is the measurement of how many times the blade makes a full rotation within a minute. Some may call this measurement into consideration when choosing an edger. Manufacturers report FPMs ranging from 10 to 150 feet. That is a rather large variance and there can be a lot of factors that affect that number.
The number of times the blade manages a full rotation may vary by the size and weight of the blade, the blade pulley system and/or engine torque. Speed can also be skewed in measurement testing. The might blade speed might be measured while edging, and at minimum or full depth. Whether the blade is being used to re-establish or maintain an existing edge, or cut a new edge, also plays a role in FPM. Bottom line, the FPM reported for a unit does not represent actual productivity or quality of cut.