12 month multiple entry Z visa - Vs - 3 month Z and residency permit??

Hi. Quick question: my future employer has asked me to obtain a 12 month multiple entry Z visa before leaving England, whereas friends are telling me I only need a 3 month Z as I will be applying for the residency permit anyway within 30 days of arrival. The 12 month multiple entry is costly and im worried its not needed. Is the school wrong or are they simply avoiding costs their end?