How do the various tools to convert a system image to f2fs work?

Recently I've been trying to install a f2fs compatible rom to my old and slow nexus7. I got as far as flashing a new recovery image and reformatting the device partitions to the new file system, but after trying to install a couple of supposedly compatible ROMs (cm11 and slimkat) and having the tablet stuck at boot I had to revert to the stock image I was running. After some googling it seems I missed a step: "converting" the ROM image to f2fs. There are tools to do that, so I was wondering how do they work actually?