That's a lie...and truth.
In quality, breeders have better birds, but in production, the hatchery will have the better producers.
They have been working on their strains for several generations and have chosen birds that look somewhat like the standard calls for...but also produce many, many eggs. They keep their lines safe by selling the chicks from the mixture of two different lines. They are just able to keep more birds that have the ability to lay eggs ridiculously well.
HOWEVER, being that these chicks are from lines that have been known as large producers of eggs, they should work very well for the purposes you are wanting to use them for.
You could do an experiment. See if your birds breeding will produce as many eggs as the hatchery sex-link within one year.