Very!! The only thing I have found they have a problem with is duck goose and Turkey and Pea's. The bigger the egg the less you can get under them, and Mine wont even try the goose or Pea eggs and it makes sense... they cant sit on those boulders... lolI was told to ask yall about how reliably broody silkie hens are?... will a silkie hen hatch out any egg when she gets the want to?
BUT as far as other breeds of chickens.... go for it!!.