A problem for me is that the OnClick event does not fire when you click on an item that is already selected. i.e. if you click on the first item, and that item has already been selected, the OnClick does not fire. I would like to change the ItemIndex to -1 upon clicking a button that is already selected.
I believe this component's name, and it's usage, were patterned after the old car push-button radios. In many of those radios you could push a button that was already down and get it to pop up. Even though the station wouldn't change, all the buttons would be up.
Fast forward 50 years or so to our Tradiobutton component. I think it would be nice to indicate "none of the above" as a choice in the tradiogroup without actually spelling out that option in another Item. If no button is lit then it is visually clear that you have not selected one of the items. Seems like a good option to me. Perhaps such a "feature" should be allowed via a property.