I realize that there is a love/hate relationship with installing an electronic item like a red dot on a pistol.
With regard to battery life, I have found the big issue is with the battery itself rather than the device.
We have no idea how long most batteries sit on the shelf. A typical 3 volt red dot battery will measure as high as 3.35 volts, and one that has been sitting a while can measure closer to 3.0 volts.
Clearly, longer life can be expected with a 3.3 ish volt battery than a 3.0 ish battery.
Before I swap mine out, I check it with a $10 DVOM and write the voltage and date on the battery with a sharpie. Personally, if it doesn’t check at a minimum 3.15 volts, I won’t use it.
This habit of checking and documenting takes no time, costs no money (assuming you own a DVOM) and I recommend incorporating it into your predetermined maintenance schedule.