The short answer
Neither option is universally better; they perform different functions. A portable camera tower can watch a broad area, create a visible deterrent, record activity, and support remote observation when configured for it. It is useful for open properties, temporary projects, and locations where a fixed camera system is impractical. Its limitations are blind spots, connectivity, weather, false alerts, and the need for a defined human response.
What to know
An on-site guard can verify credentials, speak with people, make context-based observations, patrol changing conditions, assist with evacuations, and take actions allowed by post orders. One officer cannot see everything at once, and officer coverage also requires staffing, supervision, and relief.
Use a risk assessment to identify required outcomes: continuous human presence, access control, detection, recording, rapid on-property response, or periodic deterrence. Layered coverage may place a guard at the gate while towers watch remote areas. Arrow itself says its portable camera towers supplement rather than automatically replace on-site officers. The recommendation should explain response procedures, operating hours, limitations, and total cost for each alternative.