Question about FNCCheckgroup/FNCRadiogroup/FNCRadiobutton/FNCCheckbutton

I'm migration from the FMX components to the FNC components.
I formerly used the FMX.Radiogroup and there I could add an icon to the items.

Although you can select a Bitmapcontainer you want to use on teh FNCRadiogroup/FNCCheckgroup I can't find out how to use the bitmaps.

On the FNCRadiobutton and the FNCCheckbutton I also can select a Bitmapcontainer and indeed I can select a Bitmap to use.
But when I do that my checkbox/radiobutton are gone and I can't select any choice anymore.

So my question is what's the purpose of the bitmapconainer on these components?