Even though I never played TF2, this reminds me of Ubercharge, except you lose health afterwards.
I know, its effective but when you think about it, the only effective way to use this would be:
1) a rush
2) keeping a teammate (doing an objective) alive, and allow them to do their job.
3) to use an invincible teammate to cover you.
Those are my thoughts though.
EDIT: I couldn't use letters (example a) ) like I originally planned. Turns out B looks like this : B)