1 rest used on a single player restores 15%
The group rest gives 5% to every single player in the squad and it costs 1/3 (third) of a rest.
So mathematically The % of condition restored from the packs is the same amount if you use it on every single player 1 by 1 !
But , if you use the "rest all" feature , you gonna be wasting some of that condition on the bench/reserve players.