Have been using this for a couple weeks now and have to say it works pretty well. There is a real danger of accidentally 'missing' the microSD slot and pushing the microSD card inside the cartridge which means having to open it to get it out again. The slot itself doesn't go all the way to the edge of the cart, it's kind of sunk in about 6mm.
Still, as long as you're careful when inserting the card and don't do it too often I think it's a good card.