Finally got around to starting to play with that m5stack thing I picked up at the last Maker Faire. Since my main system is linux Mint 19.1 I figured this would be straightforward.
Not exactly. No docs for linux, so I'm on my own.

So... since linux isn't supported (and the EasyLoader program is Windows-only) I've been carefully cobbling together a system to deal with it.

The actual url to install in Additional Boards Manager URLs is
https://dl.espressif.com/dl/package_esp32_index.json

There's a linux usb-to-serial driver here:
https://docs.m5stack.com/#/en/quick_start/m5core/m5stack_core_get_started_MicroPython

After running make the file seems to compile properly.
Then after reading the CP210x_VCP_Linux_4.x_Release_Notes.txt file I see I need to install the driver separately. Compiling and running the example file also seems to work properly using the port at /dev/ttyUSB0. So far so good.

The M5Burner on that same web page does work, but I'm still having problems with the Arduino IDE. Compiling code errors out with the messages

File "/home/mwieder/.arduino15/packages/esp32/tools/esptool_py/2.6.1/esptool.py", line 37, in <module>
import serial
ImportError: No module named serial
Multiple libraries were found for "SD.h"
Used: /home/mwieder/.arduino15/packages/esp32/hardware/esp32/1.0.2/libraries/SD
Not used: /home/mwieder/Downloads/arduino-1.8.9/libraries/SD

OK - turns out that enabling verbose debug messages in Preferences also shows

Pyserial is not installed for /usr/bin/python. Check the README for installation instructions.Traceback (most recent call last):

...and thus my introduction to python wheels. So downloading the latest pyserial wheel and then

pip install wheel
pip install pyserial-3.4-py2.py3-none-any.whl

resulted in a successful compilation and upload in the Arduino IDE.

Hope this helps someone out.