@klaatu
It looks like the zramctl man page should have made it clearer that the block devices it creates are compressed.
Chrome OS uses zram as swap, and it gives a pretty good compression ratio - generally around 50% from my testing, so believe those scammers who tell you how to "Download a RAM stick cheap for free" (provided you don't already have the module).
zram can be used for more than just swap - it can also be used for testing filesystems or lvm in RAM, or as an alternative to tmpfs.