Note: The Android One programme appears to be no longer active. Google has not announced new Android One devices since approximately 2022, and the programme is no longer marketed or accepting new validations. The information below is retained for historical context.
Android One and Android Enterprise Recommended were two different programmes offering a bit of overlap in security and consistency.
Android Enterprise Recommended ensures devices validated meet the minimum requirements and recommendations of a consistent UX for management, 90 day security updates for 3 years and at least one letter upgrade (O to P, P to Q.. ). OEMs maintain their value-adds, bundled apps, custom UIs and more.
Android One took this a step further; any device in the Android One programme used a system image developed with Google. Like the Nexus days of old, the UI was vanilla Android and the Android One team had to approve any additional applications bundled with the device.
Updates had to be released every 30 days and the devices had to support two letter upgrades (O to Q, P to R, etc).
When combined with AER, Android One offered additional benefits validated to work in the enterprise.
For current device procurement decisions, Android Enterprise Recommended is the relevant programme to evaluate.