they heal less than 1 health per sec?!
1.2 HP per sec, 1.596 per sec with healing T2.(possibly more not sure)
72 HP for the entire duration basicly, and 95.76 HP for the duration with healing T2.
So yes, its a after combat sort of thing, and a defensive thing that can heal rifleman shots as your dudes mow em down, not a "hey ima beat a 180 munition ranger squad!".
Basically it just increases the time the unit can stay on the field, and it is quite effective at that.
Personally for KCH and upgraded grens I think its worth it, if you think its not don't buy it.