I'd be really "easy" to land if they had an RCS, just a couple seconds worth to cancel out any lateral movements and rotations
In its current configuration, the stage can't hover: on its lowest thrust setting, the engine still provides too much thrust. So they land using a "hoverslam" maneuver where they try to decelerate to a vertical speed of 0 just as the stage intersects the barge.
There is an RCS at the top of the stage to keep the stage upright, but any lateral thrust at the bottom has to be done by gimbaling the main engine. The gimbaling angle is limited so they may have run out of control authority on this landing.