I get eggs that are medium to large. I have a hard time telling them apart from Wyandotte eggs. I haven't noticed them being any more flighty than other birds (at least anything other than Cornish which are too heavy to fly even young). I keep a few other meat breeds too Dorkings, Bresse, Buckeyes, La Fleche.
I've also not had the same issue you are seeing with the feather eating and I don't have them on an high protein diet. I wonder if its a different issue? confinement? not enough space?
genetics? the gene pool for these is tiny so I had to do quite a bit of culling to create a stock I was happy with. Up until that point i saw quite a few issues with some crooked keels and leg issues. The best stock came from someone in florida selling eggs on ebay that doesn't sell anymore. I had to breed them back to what I got from other sources to get something I was happy with.
how old are yours? they are funny and very gawky as youth but grow into exceptionally nice looking birds.
Mine are from GFF. That are about 8 weeks. I guess it's a space, confinement issue. I'm waiting for the next nice day to put them in their new coop and run. Lots of rain here lately, so don't want to put them outside when it's wet, cold and dark. I have had other breeds be flighty like this, but my favorites are calm breeds. I only have 8 so I hope I don't have to many issues with them. I will be happy if a get a decent trio out of them.