I planted some basil seeds in it some months ago: they got to about an inch tall and just stuck there. Yesterday, I gave the pot 4 rabbit droppings and watered them in. Today the seedlings are already noticeably taller!
Might be suitable for planting something like alpines that don't want a lot of feeding, but not good for bedding plants or anything that actually needs feeding.
However, it does seem to drain well and has remained free of fungus fly, which is a plus. Might be suitable for use mixed with the rich compost from the worm bins, or rabbit droppings.