i did some testing, and it does seem to only work with the LG Messaging app. I tried one of us having Android Messages, and both of us having Android Messages, and no dice.
I have the double checks only with those on same cell network. U can go to settings (3 dots n top right) on ur msg list..go to texts..then more & just disable "read reports". That keeps whomever U txt from knowing U received/read their txts.