Uh, I forgot that, Online Nandroid Backup only makes the backup, a recovery is still needed to restore, so, it's useless for you. You'll have to stick with adb backup then, it'll backup most of your apps and data, but modifications you made directly to system (buil.prop changes, files flashed with Flash Gordon, etc) will be lost...
Sony Xperia M dual [C2004]
ROM: 15.5.A.1.5 (stock)
Android version: 4.3 (rooted)
Bootloader: locked (unlockable)