kinda useless..if it remained with a higher percentage for a longer period of time the higher its level..i would find that a bit more useful..for example, the antidote protects you for 2 minutes..using that case, level 2 would increase the time to 3 minutes or something; level 3, 4 minutes; etc..
This one is very useful in some cases - Family Battle, as an example. Or this zombie event: LootLady used a PowerPack to get her bike, now we can use this. It's very specific
At 650% (with crew bonus) i could burn through my 3k stamina only red icing people and still not be dead lol... it's a bit excessive. It will save me using my 'useless' cash though...