Not as common as you might think. The PCB's are of very good quality and look great. The one I've tested work as they should. And no, I have not tested all of them, as there are 147 individual units per 100 x 100 mm surface. And 10 of those. This means that I can put led-lights in 735 N-gauge locomotives. Enough for all members of our club and "a few" to spare for others. This would have been possible without Elecrow. So I'm a happy customer and will gradly return.