A hair cutting device kit comprising: a drive unit configured to receive a cutting unit comprising a follower element; the drive unit comprising: a drive for driving a cutting unit mounted on the drive unit; a cutting unit having an extension mechanism configured to vary a cutting length of the cutting unit within a cutting length range; an actuator configured to cooperate with the extension mechanism of the cutting unit to vary a cutting length of the cutting unit within a cutting length range, the actuator being moveable between a first actuator position corresponding to a first extreme cutting length of the cutting length range, and a second actuator position corresponding to a second extreme cutting length of the cutting length range; a user-moveable control element moveable between a plurality of control positions including: a range of length control positions between a first control position corresponding to the first actuator position and a second control position (62") corresponding to the second actuator position; and an off position corresponding to deactivation of the drive, wherein the off position is adjacent the first control position; wherein the cutting unit comprises a follower element configured to drive the extension mechanism and cooperate with the actuator so that, when the actuator engages the follower element, movement of the actuator between the first actuator position and the second actuator position causes corresponding variation of the cutting length between a first extreme cutting length of the cutting length range and a second extreme cutting length of the cutting length range; whereby in use the actuator is in the first actuator position when the drive is deactivated by movement of the control element to the off position; wherein the cutting unit is biased to return the follower element to a first follower position corresponding to engagement with the actuator in the first actuator position; and wherein the cutting unit is detachably mounted to the drive unit. a drive unit configured to receive a cutting unit comprising a follower element; the drive unit comprising: a drive for driving a cutting unit mounted on the drive unit; a cutting unit having an extension mechanism configured to vary a cutting length of the cutting unit within a cutting length range; an actuator configured to cooperate with the extension mechanism of the cutting unit to vary a cutting length of the cutting unit within a cutting length range, the actuator being moveable between a first actuator position corresponding to a first extreme cutting length of the cutting length range, and a second actuator position corresponding to a second extreme cutting length of the cutting length range; a user-moveable control element moveable between a plurality of control positions including: a drive for driving a cutting unit mounted on the drive unit; a cutting unit having an extension mechanism configured to vary a cutting length of the cutting unit within a cutting length range; an actuator configured to cooperate with the extension mechanism of the cutting unit to vary a cutting length of the cutting unit within a cutting length range, the actuator being moveable between a first actuator position corresponding to a first extreme cutting length of the cutting length range, and a second actuator position corresponding to a second extreme cutting length of the cutting length range; a user-moveable control element moveable between a plurality of control positions including: a range of length control positions between a first control position corresponding to the first actuator position and a second control position (62") corresponding to the second actuator position; and an off position corresponding to deactivation of the drive, wherein the off position is adjacent the first control position; wherein the cutting unit comprises a follower element configured to drive the extension mechanism and cooperate with the actuator so that, when the actuator engages the follower element, movement of the actuator between the first actuator position and the second actuator position causes corresponding variation of the cutting length between a first extreme cutting length of the cutting length range and a second extreme cutting length of the cutting length range; whereby in use the actuator is in the first actuator position when the drive is deactivated by movement of the control element to the off position; wherein the cutting unit is biased to return the follower element to a first follower position corresponding to engagement with the actuator in the first actuator position; and wherein the cutting unit is detachably mounted to the drive unit.