I saw these in Germany and I knew had to grow them. I found the seeds online without all that much bother (but enough) and for $10 they generously sent me about 8 seeds. I’ve been waiting and waiting for them to ripen. They are taking their goodnatured time about it. On the other hand I don’t really know how you know when black tomatoes are ripe. But for a start they are hard as rocks and, like peaches and nectarines, a crunchy tomato is morally objectionable to me.
It turns out that only the side facing the sun gets black so when the green underside turned vaguely red, I picked one. I could tell it wasn’t exactly ripe it was softer than the others but there was some give. It was ripe enough and it was delicious.