I found out more information. The dust is NOT recommended for watering feeders. All other sizes are safe for providing drinking water to feeders. Also, any size crystal can be cut up and reduced in size. The expert said it would be easier to cut them up while hydrated instead of trying to crush them while dry. But with the option of ordering the different sizes it may not even matter to most. With my limited experience I would think the large ones would work perfect because they get bigger and more can fit in a smaller lid without small pieces falling out everywhere.

Just gives options for people who like them and might want different sizes. Only reason I would order from them would be to get enough to do some serious gardening. A couple months away and I am not sure I am ready to get that involved with my gardening this year.