What is a "heritage breed" really? There's so much talk about heritage vs hatchery, but heritage breeds aren't what they used to be. Go look on any thread here and you'll see arguments over what the sop is, how it has or hasn't changed, etc. Breeders have different goals, some breed for meat and others for egg production. Even on this thread, @cactusrota and @DesertChic breed NN's and may have similar but not identical goals for their breeding projects. They may or may not care about color of the bird, color of the eggs, etc. Not that cactusrota and DesertChic are arguing over anything btw, they're just both working on NN's and may have different goals.
The RIR should typically lay 4 eggs a week and is supposed to be a dual purpose bird, so they should big enough to eat. My RIR's from a hatchery don't come close to the weight for a standard bird but they lay eggs EVERY day. I bet they don't weigh more than 5ish pounds with their feathers. Same for my Australorp. Yet my Aussie girls that I got from @BlueBaby are bigger birds now at six months than ALL of the one year olds I got from the feed store. Are they heritage birds, or are they just better quality due to breeding practices than the hatchery girls?
I haven't had the opportunity yet to track how many eggs my young Aussie girls lay, they've just started this Spring, so to test things out I'm tracking egg production from just the Aussie girls, including the hen that came from a hatchery, once I can figure out which newbie lays which egg. I'm thinking about trying the food coloring bit on their fluffy butts.
Realistically, there's no such thing as a pure bred chicken, unless you go back to the jungle fowl they came from. Heritage breed or not, they've pretty much all been crossed with something to improve the original for one reason or another.
What you want from your birds is how you should make decisions. Do you want an egg laying machine, or eggs and meat? Will you cull the girls when they don't lay, sell them off to someone who will? Do you care that with egg laying machines you may have to cull on a regular basis? How do you feel about hatcheries and what they do, hatching and selling as many chicks as they can to make a profit while killing off the roos.
Different people have different reason's of why they want to have the chickens. Just keep in mind that either way from a hatchery or from a breeder, most of the roosters get culled. From a hatchery, they just get culled earlier as new born chicks. Many breeder's wish that they could be able to tell right off the bat who the boys are also, and I think that many of those breeders would also cull a bunch of new born boys, rather than to feed them. Who needs a yard full of roosters, unless you are planning on eating some?