I imagine between the efficiency of the LEDs and the lower heat (less use of the mini-split), those lights should eventually pay for themselves.
Was there any adjustment you had to make in terms of monitoring the heat after the switch, or was the system able to easily compensate? When I grew in a somewhat insulated garage, after I switched from HPS to COBs I had to add heat to the room in the dead of winter. Now I'm down to a single tent in the house, but similarly I'm still using those 'old' COBs, and haven't upgraded to QB's because I would need to add heat to the tent if my system got any more efficient.