Personally I use a tactical flashlight at work as a police officer. With this background, these are my factors to consider, when I buy a new duty flashlight:
1. reliability.
2. reliability.
Yes, that is the most important thing. The light has to work. I don't want to think about, if the flashlight may fail on duty.
3. easy to operate.
Same thing. The light has to work and I don't want to think about, which button I have to press how many times. Start with high mode every time, easy to switch modes. No bells and whistles, no fancy stuff.
4. Lumen output / beam distance / runtime
Well, these should be at a reasonable level. No dragster with a crazy amount of lumen, which will decrease the runtime, increase the chance of killing the driver or other components, blinding myself,... Depending on the beam pattern, about 1000-1500 lumens in a medium wide beam with good capabilities in short to medium distances is a nice package for a edc-duty-light carried on the belt.
5. size
A edc light should have a small head. We have to carry a lot of things on the belt, the seats in our cars are quite narrow - the smaller the light is, the more comfortable it is for me. A flashlight, which is carried in the bag in the car can be bigger.
6. price / brand..
The brand is not this important. But I buy lights from brands, which have a good reputation or have proven, that they are able to build good flashlights. Regarding the price: of course it is a difference between paying around 100 EUr or 300 EUR. In the "normal" price range (100-150 EUR) I am willing to pay 10 EUR more for getting the better light.
If some lights are on the same level, then some other aspects will decisively: anti-roll feature, very grippy design (not slippery, e.g. rubber used on the 360x1), led tint....
greetings
Michael