Why buy ais receiver when app is free?

For me, even disregarding the transmit function warning others of my position, the critically useful part of my AIS receive signal feeding OCPN are the CPA and TCPA data. They inform me of actual real-time threats and give me safety-critical information of the window when to dodge through the busy shipping lane ... which is when it could be when the mobile signal would be fading.

Anything else is just a toy - and worse if it induces a sense of security when none such exists - especially when the data relies on amateur receivers with less than 100% serviceability.
 
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