Back To Black/Kill of The Night (Amy Winehouse & Gin Wigmore a cappella cover) 

SHE IS and they're doing great i love the mashup of two of my favorite artist

They're often unreliable for this kind of setting because of the sheer amount of people.

Good question, so with this amount of mics it can cause interference with each-other over the radio frequencies, and there is also less latency with wired mics, like Nano seconds. Also wired mics are a hell of a lot cheaper lol