breeder boxes/nets bad
Breeder box/nets, IMHO tend to stress the females to the point of aborting their fry or even kiling her. I have not seen much luck with these things in my years of breeding livebearers. I find that mother and fry do well in a heavy planted tank.
But guppies will breed fine and not even eat the fry if you have plenty of hiding spaces for the fry to hide in. The best thing to do is have a heavy planted tank. I love using hornwort, its very easy to get ahold of and its cheap (plus it grows really fast). it is a floating plant and it gives the female a place close top to hide and relax. Guppies, are a schooling fish, and they tend to be happier in a group. So when they are cut off, or alone they tend to stress out.
heck, I had a 29 gallon tank for over 5 years, that I never bought a guppy to replace and it was constantly filled to the point of almost being over stocked with breeding guppies. The other fish I had in the tank were cories, siamese alage eaters, and amano shrimp. It was a very nice planted tank.
jim