Instruments such as the turn co-ordinator are gyroscopes. Gyroscopes "topple" when thrown around by an aircarft doing aerobatics. They then take several minutes to resettle, before they give true readings again. Some gyroscopic instruments can be "caged", before performing aerobatics, to stop them toppling, but they do not show a correct reading when caged.
A turn indicator is not a gyroscope (but don't ask me the techie stuff on how it works
). Therefore a turn indicator cannot topple, so gives a correct indication during spinning & other aerobatics.
I hope that helps, but perhaps the techie experts can give you more info.