These interlocking grids with 3/4 inch square openings, are useful to use in kennels that house the smaller dog breeds. Not strong enough for really heavy weight dogs, they do just fine for the small to medium sized dogs.
They can also be used to place in whelping pens, though I would suggest if you do that you also cover them with something like the Drymate whelping box liners, which are comfortable for the mother and the puppies, and are comfortable for especially the smaller pups to get around on.
I personally think these do better in kennels or pens that house your dog temporarily. For more permanent use, I believe that the dogs are more comfortable with something a bit more solid underfoot. Still the price and the portability of these do make them an attractive option for your pens.