Yu have to select them just after loading finishes or just before loading starts , i can't remember. Yes, they are one time boosters and disappear once hey are used, but don't worry use them, they keep popping up after every match. Its not like they are difficult to get, in fact I don't wven how I earn them but there are a lot to choose from before every match
! Its a mechanic borrowed from mobile games.
I started my new game + finally now that my upgrades finally got carried over correctly. Now I know why ppl could finish th egame in 14 /16 hours while I took 24 hours. Its because th eListen mode kills all scouting around and checknig out enemy positions and/or any randomn firefight. Its just a matter of 'ok, here are all the enemy positions, lets start from the this side '. Thank god, I had turned it off on my first playthrough.My experience wouldn't have been half as entertaining or atmospheric. The game is very well tested without it. With listen on, I am actually finding the game a bit boring....I thikn I will just turn it off.
BTW, its nice to have a Shiv which works for three kills before breaking, right from the beginning
! Uptill now Listen mode has ensured I don't need Shivs, as grabbigb an enemy from behind just does the trick. Saving it up for doors and clicker atracks once I earn Shiv Master ability.