Weird, that seems to work fine here. I'll do some more testing later. Are you on Mojave?
// ah I think it's sometimes not updating the icon - could you verify that if you assign different colors to the control strip buttons, these are updated everytime?
//no, that only happened when I didn't assign a icon to some of the widgets
"Add only one" just means that you can not have more than one custom Control Strip button visible at a time. If you define multiple for one app it will be random which one is used.
I just uploaded v2.662 to fix the Touch Bar toggling, but I can't reproduce the "not updating" issue yet.