Transplanting a seedling from the APS-24 is very easy. There is a hole at the bottom of the cell that is used to connect the soil mix with the capillary mat so that water can transfer. Just stick your finger through the hole and push. The cell pops out and the moisture in the soil mix enables the soil mix to retain the shape of the cell.
Then it is a matter of placing the cell into the APS-6 unit and putting soil mix around the cell so that the seedling is in the middle.
Ease in transplanting is one of the main reasons I use the APS system despite the problems I have with Algae growing in the unit.