Audio monitors do one thing well: they let you hear a cry from another room, cheaply and reliably, with minimal setup and long battery life on the parent unit.
Video adds visual reassurance — seeing your baby is genuinely calming for a lot of parents, and it helps you judge whether a noise is actual distress or just baby chatter, without you needing to go and check every time.
The honest trade-off: a video monitor screen is another thing to check compulsively, which some parents find increases anxiety rather than reducing it. If you know that’s you, audio-only with a good speaker might genuinely serve you better than the higher-spec option.