Lin Sends Away for a Hot-Cold Serving Tray She Has

Essay

Lin sends away for a hot-cold serving tray she has seen advertised. The tray is promised to keep hot dishes hot and cold dishes cold without electricity. Lin tries it out by placing a pan of hot beans on it. They stay hot throughout dinner. "It works," she tells her husband.
Do you think there could be a better test of the hot plate? Explain your response in a sentence or two.