EMS - Why ?

What should i look when i go buy a EMS ?
I´m asking because theres EMS start a 50US$ until 300US$ !!

I just wanted to ask why are a lot of people so much intrested in EMS. Is it that important. If so then how do we use it??? And How does it effect us?

Yeah !!!
It is a good question.
Tks for “lend” me the english.