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Yes, it can be used, but there's a catch: it drains tears instead of blood. And we want to level up with blood, and as quickly as possible!
Also, it seems to me that the blue numbers (skill effects) depend on the level of the upgrade. I haven't checked yet, it's just an intuition... but I'll be VERY disappointed if it turns out not to be true.
P.S.: I'm playing the first mission for Inferno, warrior-blood build. On hard difficulty. I haven't completely defeated any players yet, but I've already chosen the blood path (leveled it up to 300, even without a cheat with Lilim). At the same time, the tear level is 0 (zero) ;) This means that I haven't joined any neutral squads (you get 10 tears for that right away), so I had to kill them all.... that's how I'm playing, crying and killing, those succubi, doggies, madmen.... killing and crying :)))))))))))) It's not possible to fight without any losses, but the single madmen save the day. So the tactics for Inferno haven't changed much since the fifth game :)