Is it time?

Hi guys, I'm just wondering when to use the ultimate crit card... I unlocked Tier 14 Wave 50 today. Is it a nice to have or a must use card? Would it be helpful for my ultimate weapons right now?

Hi guys, I'm just wondering when to use the ultimate crit card... I unlocked Tier 14 Wave 50 today. Is it a nice to have or a must use card? Would it be helpful for my ultimate weapons right now?