I have run an experiment on an old Samsung smartphone (Android 4), and it runs perfectly, but I would like to extend my project by testing several participants, so I need several similar smartphones for other experimenters. The problem is that it is difficult to find an old smartphone always running on Android 4 (as OS does not work on more recent version anymore). Do some of you have previous similar experience with Android testing on smartphones? I read that Windows 10 tablets were another option, but we would really like to continue to use smartphones because they have smaller screens and I didn't succeed in downgrading recent smartphones to previous Android version..
Many thanks for your help !