Thanks folks. I got them to add a different egg colour to my flock. They are kept with Lemon Cuckoo Niederrheiners (pale egg) and French Splash Marans (dark egg).
I just got them a few weeks ago but from past experience, I've found buffs to be both better layers and broodies. I'm importing some large and bantam whites from a top breeder in England next week.
I've been offered a trio of Gambels. I have never kept them before. They are two years old. Can anyone tell me how old the hens will be when they stop laying?