Well, you should probably wait and see just how good or bad that flashlight is before you buy anything else. LG makes a pretty good 365nm LED but that doesn’t mean you can just drop it in that unit.
What do you want to be able to do with your UV flashlight? The one you’re getting might still make stuff glow pretty good but will have lots of left over visible light.
If that filter you ordered doesnt fit, try looking for a “convoy S2” with a 365nm led already in it…
You might look for some threads here by “djozz” where he reviewed different UV lights and emitters, like these: