Sizzle is a feather type, not a distinct breed. I'm not sure what sort of development has been done with them, but I've always been told breeding two sizzles together was a bad thing to do, and two sizzle genes made a very ugly bird with possible other issues. So I don't know how that could be developed into healthy true to type birds with strong feathers.
I've never kept or bred sizzles so all I have is hear say. I might be totally wrong about breeding them, but I know I'm not wrong on calling it a feather type.
Again thank you. It seems obvious that these terms are vague and hold different meaning depending on the person.