Instant kill works fine for me, although it cannot be used when double damage is enabled (I guess double damage overrides the instant kill setting?).
I've been using this for a while and I've noticed that when having instant bullet enabled, my bullets seem to have a limited range, meaning that I am not able to shoot those who are far away. I dont know if this is because I'm doing something wrong, or if the cheat works that way.
Another thing I noticed is that instant kill or double damage doesn't work work for vehicles. I would love to see this feature added if you plan to still keep working on the cheat!
Anyways, thanks a lot for your work!