if masked materials look good use them, as the opaque parts will prevent overdraw. Could mix masked and translucent particles together in the same system, keeping masked particle toward the center of the flame and translucent on the outskirts.
I’ve heard additive materials are slightly cheaper than translucent, but i’m not certain if thats the case.
gpu particles are generally cheaper than cpu ones. not sure how many phones support gpu particles though.
Using particle cutouts on sprite particle can reduce overdraw.
overdraw cost will vary based on how much of the screen is covered by the translucency. Because things get smaller when you get further away from them, if you can prevent the camera from getting too close, that helps. Could also reduce the number of particles spawned whenever the camera is right on top of the particle system.
use LODs