ChromeOS Flex Compatible with MacBook Air - External HDD 320GB

I tried installing ChromeOS Flex on an external HDD with a MacBook Air 2013.
Seagate ST320LT020-9YG142 320GB
According to CrystalDiskInfo:
Power-on count: 540
Usage time: 520 hours
Health status: Normal (Image 6)
When you hold down the Option key and turn on the power,
then select the external HDD,
you will see the ChromeOS Flex setup screen.
Please continue the setup with your own Google account.
I tried setting it up twice with my own Google account.
After that, I reinstalled it.
USB to SATA conversion cable is not included.
Due to the nature of the product, returns and refunds are not possible.
This is for those who want to try ChromeOS Flex. Thank you.
I am also listing the same HDD as an internal HDD for Windows.