What is the difference between Salesforce Usage Metrics and AppExchange App Analytics?
Usage Metrics was the first official API introduced in 2014 for Salesforce ISV and OEM partners offering insights into their application usage. It exposes a daily snapshot of custom object statistics per subscriber organization (e.g. "How many records of type MyCustomObject did exist on a given day) along with daily view counts for Visualforce pages. See the official documentation in the ISVforce guide.
AppExchange App Analytics, introduced in 2019, is the newest official API to retrieve usage analytics for managed Salesforce packages. In comparison to Usage Metrics, it exposes a wider and more granular set of data. See our in-depth documentation about App Analytics.