Just wanted to add another trick that has have applied. Add a perforated shelf liner to the bottom. This gives some added traction, as well as prevents small chicks' feet from getting caught in the small openings.
You want the perforated style to allow air movement, and humidity to...
If you are going to incubate duck eggs often, I suggest to modify the tray by cutting out every second divider. This way you can fit 8 eggs at each cycle. You would still be able to use with chicken smaller eggs, by (placing 2 eggs into larger slots) Or purchase a replacement grate...