Hello!

Responding to modumb,
Sorry to others, has no relation to the title of the post

I had to use extroot on my AR750 Creta. Only free150kb after installing 3.201beta2. 0227 firmware and it was impossible to install anything else.

I had al old 512Mb USB Pendrive and it’s very easy to make it as dev/sdb1 >>/overlay in Luci>System>Mount Points, I’n not an expert in OpenWRT and also no trouble with UI so far.
But I had to make extroot right after fresh clean firmware update and no internet at all to maintain those 150Kb free in AR750. After that I made restore and I install the .ipk plugins I had previously.

Be sure to reboot after extroot and see the sdb1 /overlay working or in Luci>System>Software the increased free space of your USB or SD Card (SD Card maybe is named /sda1)

Bye