Take into account when InstantRestore can or cannot be used:
InstantRestore is not available for all restores as not all properties are supported; for example, you cannot restore a SQL Safe backup from a TSM Server.
InstantRestore supports only complete database restores and does not support file or filegroup restores.
InstantRestore can only work when you choose a Fully Accessible recovery state.
InstantRestore does not support native format files.