In which area would a unitary system work best?

Unitary system is best suited for small states or homogenous states with similar regions as in the case of Zimbabwe where there is a population of about 13 million people.

Explanation:

Although political power may be delegated through devolution to regional or local governments by statute, the central government may abrogate the acts of devolved governments or curtail (or expand) their powers. A large majority of the world's states (166 of the 193 UN member states) have a unitary system of government.

A nation state with a strong sense of national pride or identity

see below  

explanation:

all of the above