Have any of these companies developing Android 6-based devices done anything to mitigate the security flaws in the software? The hardware sounds compelling, but older versions of Android are as porous as a sieve, security wise.

Note this recent advice from PC Magazine, in their 2019 Android phone buying guide:

"For most other phones, Android 8.0 Oreo is the current shipping version, and you should find it on most phones today. Do not accept any phone with a version older than 7.0 Nougat, as the older the Android software version gets, the more likely it is to have serious security flaws."