I am usually reluctant to sing unaccompanied.

IMHO you have to have a much better voice (bel canto voice) to be as pleasing to the ear as a solo unaccompanied singer than either as a harmony unaccompanied singer or any sort of accompanied singer.

Part of the big problem in persuading the audience to accept solo unaccompanied singer is that there are (I fear) more who think they can cut it as a solo unaccompanied singer than actually can.