I don't feed suet to my girlies but I tell you what, you throw some bread into a skillet with some bacon grease and give it to them and watch them go nuts.
I feed it too, sparingly, because it can make their poops a little greasy if they overdo it. I mix ground suet with various things- flax seed, cracked wheat, sunflower seed, unsalted nuts...sometimes I bind it with a little lard or peanut butter. I use it during extreme cold to buffer their systems.