A string trimmer, also known as a weed whacker or strimmer, is a garden power tool that uses a rotating monofilament string to cut grass, weeds, and groundcover, especially in areas a lawn mower can't reach. 

LST201: 10” string trimmer and the  The LST320C  9,000 RPM 

LST320: 12” string trimmer, it uses a more powerful motor to swing the longer line. will feel more powerful and will accomplish more work, faster with the larger cutting area. 6,200 RPM

However, given the difference in swath length, an exact comparison won't be accurate.