Large Full frame (35.8 x 23.9 mm) sensor Large sensor in Leica M10 ensures a good low light image quality compared to smaller sensor, and it also provide shallow depth of field and a nice blurry background when needed.
Medium size Body With relatively smaller body compared to DSLRs and better ergonomics compared to Compacts,Leica M10is a good compromise between size and functionality.
660g Carrying this weight all day may not be very comfortable for you.