Thanks for all the replies, things are a lot clearer now. The point of my original question was to clarify the situation about inadvertent spinning during aerobatics, especially inverted.
So it wasn't academic as far as I am concerned, as I intend to move more seriously into aerobatics, and the particular aircraft involved has a Turn Coordinator. It seems that, for peace of mind, I should get a Turn Indicator installed. Now the question is, should I replace the TC with the TI, or have it as an additional instrument?