Using 'eye up' suggests a strong interest or desire for someone or something.

Desire Implied

'Eye up' can feel intrusive if used about a person, as it may imply undesired attention.

Slight Intrusion

'Eye up' is casual and might not fit in formal contexts. Use in everyday, relaxed situations.

Suggests the person is making an estimation or judgement, not just looking.

Often refers to a judgment based on physical appearance or observable qualities.

Can imply a quick, visual assessment leading to a prompt decision or course of action.