Flashing an ISO image to an external drive like a USB stick or an SDCard is a common way to get up and running with a new system. The "classic" way of burning this to a CD-ROM is not really in use anymore. Still, many projects do provide images as ISO files.
This lists working approaches on MacOS to handle this task.
Overview of disks
A quick way to list the devices is to use diskutil:
$ diskutil list
It should show something like the following output:
/dev/disk3 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: FDisk_partition_scheme *8.0 GB disk3 1: 0xEF 36.7 MB disk3s2
In my case this is a small SDCard which I entered.
Flashing the external drive
Flashing is best done using the command dd. I got good results with the following command line:
$ sudo dd bs=10m if=image.iso of=/dev/rdisk3
Note
Notice that I am using rdisk3 instead of disk3. This should increase the throughput a good chunk.
Monitoring status
dd has built-in status reporting on the command line, just send the signal INFO and it will print out the current status:
$ KILL -s INFO $PID_OF_dd