I have tested the V4 mod on both xperia Z and ZR. No issues or bugs found.
My suggestion is NOT to install the S-Force option because it simply sounds horrible once activated (On xperia z at least).
I also tested the backup-restore function. Works as it should.
Hint for ZR users: unlike XZ, the main speaker is twice as powerful, so i advise a setting around 70 for main speaker and 79-80 for earpice. that should balance it.
On XZ i use 73 main speaker and 79 earpice. with custom 82 on both for ringing.
So that's all folks, stereo for everything, fm radio, media, you name it, now with backup function.