i am not sure they will send you back with 2x bonuses. it has high risk to do, if you do it maybe you can lose your 0,5 ETH.. please do not believe everything that requires the payment of balance because it has risk of scam. better you can choose another way like join airdrops or bounties it will bring profit than you sent your balance
If you decide to send your coins to websites like that I can guarantee you are never going to see that money again, this kind of scam is nothing new and people have been falling for it forever, anyone that could double your money in a matter of hours will not need the investment from anyone else and if he was just a charitable person trying to help others then he will not need that you send money to him in the first place and will just ask for your address, then we can safely conclude this is a scam.
exactly, if he really makes an amazing promotion then it is not possible they ask you to send any coins in this case ethereum, because with you only sending the address is enough and safe to do a big promotion with a reasonable reward with something that might be able to be different from the reward that will be obtained. so don't ever believe in promotions that ask you to send coins to them because clearly it is a scam