im not pushing for your zenfone purchase, pero i commend their after sales support.
when i bought a fonepad 7 back in 2014, i had issues with the OS repeatedly unmounting-remounting my microsd. tried everything i could to fix it. was so pissed when it finally corrupted my microsd. i contacted asus' support using the app pre-installed on the phone and the rep i corresponded with was very helpful and i got my phone fixed within a week(via OTA software update). she even followed up asking if i am still having the same problems after the upgrade.
TIP: if you are to contact a support team reporting an issue, make sure you have scoured the internet for all possible fixes. what i did is i detailed all the layman troubleshooting steps that i have tried and also provided links of all the discussion groups that raised the same concern. it became the basis for their group to conclude that the issue is not isolated to just one unit.