It's a slush box that makes changing gear manually easier than a conventional auto. Change order is P R N D. Once you get back into Drive the lever can be tapped left or right to change down or up respectively.

It does have a trick that if you hold the lever to the left (as opposed to tapping it left to change down) HAL will decide which gear will give you the best torque for your current speed and change down to it. It's useful for overtaking on single-carriageway roads.

As with any slush box vs manual debate, ultimately it's what you're happy with.
A