Heres a little on what the net looks like and what it's purpose is.
Depending on the fish you are breeding, I would get a plastic breeder cage. You can see the fish and i just think that they are more convienient. Like i said, it depends on the fish, for cories they are very small and mine always fell through the cracks in the plastic cage, so i used a net. Or you could get both and depending on the situation decide which works better.
i would personally use a net breeder for a couple of reasons:
1. more water circulates throughout the breeder
2. they don't have slits for other fish like gouramis to grab tails through the bottom and have a snack
3. they're bigger than most plastic ones.
Neither of them are ideal, because they can greatly stress the mother fish out being in there. If you're going for just keeping the fry in there, net breeders are your best bet. stargirly1208 pretty much summed up why. Fry tanks are always going to be your best bet, because you can;
Put the mother in there and let her give birth without the worry of stress.
Raise the fry without fear of other fish eating them.