Just got it updated, check the updated mod's description
I found it to be well rebalanced without any quantity

It would be cool for the injector to be 100% slow to apply, and 10% fast

In DayZ energy is a synonym of food (at least in code), but I got what you mean. I'll add a stamina injector ( mii_injector_stamina ) + add a variety of 10-30-50-100% for all injectors and/or maybe I'll change it to be quantity based so it'll be easily configurable :)

mii_injector_energy - maxes out the energy value

it gives food, not energy or stamina

I think it should restore stamina and a short duration of action should make it possible not to waste stamina

mii_injector_health - maxes out the health value

For health, it would be great to make 10-50-100% hp 3 injectors. 10% is used instantly, 50% is slower and 100% is even slower so that there is a balance. Now the injector instantly gives 100%, this is a bit of an imbalance