Compatibility summary
You will need a travel adapter in Montserrat; plug types used there differ from South Africa.
Plug comparison
South Africa plug types: C D M N
Montserrat plug types: A B G
There is no common plug type between South Africa (C D M N) and Montserrat (A B G). You need a travel adapter.
Voltage comparison
South Africa: 230V, 50Hz
Montserrat: 230V, 60Hz
Voltage difference is within a range many devices tolerate; check your appliance label.