I received my crs309 today. And the setup was nerve-racking. I read plenty of stories on setup, and they all talk about log in with ‘admin’ no password. After at least an hour, I found that there’s a password on a sticker on the bottom of the device. Then I took me a couple of hours to find to change the device mode to sitch to swOS. It finaly worked out.
My swOS on the device is 2.7 and a new version 2.18 is available.
I tried the ‘download & upgrade’ button. the response is downloading and reboot. The device reboots but the firmware version is still 2.7. After that I tried ‘file for upgrade’ option. Downloaded the file from mikrotik. Selected the downloaded file and the upgrade process continued. After reboot the firmware is still 2.7.
If you want to upgrade, 2.16 should be OK, but don't take this statement as guarantee of any kind.
In any case - again for the moment - do not upgrade Ros to higher than 7.19.6 (better be safe than sorry, though I haven't seen reports of briocked devices, it seems like 7.20.x has some issues in functionality, particularly using Webfig/browser).
