I remember someone that posted here some kind of doubler in 48 hours,i had invested some penies i had on my account and guess the result he achieved around 400 btc from people and closed the deal,i know that they scam but the ammount risked were soo high that i cant stop smile,but be sure all those projects scams.Try exchange at altcoins you may double your coins but not from one moment to other.
yeah i have used these sites once or twice in my life.
but i have only used them for "gambling purposes". for me it is like rolling dice with an extremely low chance of winning. but in the end i think you are better off rolling dice on 2x with ~50% chance of winning.