The main difference between the "Logitech Signature M650" and the "Logitech Signature M650 L" (which is often referred to as "M") lies in the following aspects:

## Size
- The "Logitech Signature M650" comes in a medium size, while the "Logitech Signature M650 L" offers a larger size to accommodate different hand sizes.

## Dimensions
- The medium size measures approximately 108.2 mm in height, 61 mm in width and 38.8 mm in depth, with a weight of approximately 101.4 g.
- The large size measures approximately 118.7 mm in height, 66.2 mm in width and 42 mm in depth, with a weight of approximately 115.4 g.

## Comfort and ergonomics
- Both models have a contoured shape, a soft thumb area and rubber grips on the sides, but the larger version offers more space for larger hands.

## Availability of left-handed versions
- The "Logitech Signature M650 for Business" is also available in a left-handed version, which is not the case with the standard version.

These differences allow the mouse to be better adapted to the individual needs and hand sizes of users.