I've heard several stories about this. 1) they do fine for a while then crash and burn due to excessive fat internally, 2) they do Ok laying but simply get so heavy they start having trouble walking around, 3) they seem fine and lay normally but drop dead suddenly 4), they do ok but stop laying early, and 5) they do Ok. Their chicks won't resemble them, but it's all an experiment.
IIRC double yolks are seen more often in heavy breed hens.
ETA: direct from the Freedom Ranger website
I am looking to rebuild a dual purpose flock for both meat and eggs. You market your freedom ranger chicken as a broiler, but they look quite a bit like a number of standard "heavy breed" chickens. Would they be suitable as a laying chicken as well, or as with more conventional broiler breeds would it be unwise to keep them to peak laying age?
They will work fine as a dual purpose chicken if you do not allow them to get too heavy for laying.
IME, keeping their weight under control is a little difficult
I have one that looks good, but the other may end up Christmas dinner if she gets any heavier.