ZIA - Internal GRE IP Range vs Unnumbered IP?

Hi all,

While i am trying to start GRE Tunnel Configuration in ZIA, i observe there are options to choose between Internal GRE IP Range or Unnumbered IP but not sure what is the pros & cons,impact, prerequisite, etc.

Configuring GRE Tunnels | Zscaler I read zscaler reference but not much insights provided. Could anyone explain more on this please?

Many Thanks!!!