The difference with these pallets is that they are made with sled instead of square supporting pieces. That means that the forklift can use them only from two sides, not four.
On the other hand, they can carry more weight since it is more evenly spread all over the pallet.
Double-face pallets are made up of decks on the top and bottom. The bottom deck feature makes the pallet stronger and helps distribute weight evenly. There are reversible double-faced pallets that can be used on either side, top, or bottom. Non-reversible versions have one side with more planks for prolonged storage