Bought, downloaded and successfully installed on my F5121. Didn't needed any Emma tool as my device came updated to version 34.3.A.0.238 (although 34.3.A.0.228 seems to be sufficient to not having to use Emma), I could just flash using the script (after unlocking the bootloader of course).
Device booted fine and I could install the extra apps (Alien Dalvik etc) from the Jolla store.

Just now I realize how much effort I put into customizing my Aquafish / Jolla C. Now to install all those apps, tweaks, adjustments etc....