Fall damage is cancelled for you. On landing, it is converted into area damage: up to 4 ❤ within a 4 block radius, in proportion to the height of the fall.
The Stomper turns every high platform on the map into a weapon. You have to learn the jumping spots, and to aim at a group rather than a lone target: the impact hits everyone.
With no height to drop from, it is an ordinary PvP kit — its value depends entirely on the map.