How common is ARM NEON support among recent Android phones and tablets? Some ARM processors support NEON extensions for acceleration of certain maths operations useful in multimedia, 3D graphics and the like.

How common is NEON support on Android phones and tablets made in the last three years (since 2016)?
To get Google Play Services, devices must follow Android Compatibility Definition Document and since Android 6.0 - Native API Compatibility has required Advanced SIMD (a.k.a. NEON):


  MUST include support for the Advanced SIMD (a.k.a. NEON)


Android 6.0 was released in October 2015. So if the device originally sold with Google Play and included Android 6.0 and up, it should have NEON support.

Realize that older devices sold with older versions of Android didn't NEED to have that requirement but by that point most mid-tier and high end devices had NEON support.