if you put your money in futures, it's not an investment, but it's trading, because even if you put the lowest possible leverage, there will still be the potential for a margin call. so it depends on you now, whether you are ready to risk €100 into the futures market, if you are ready then go ahead and put your money in futures trading. however, if you are not ready to lose that money, you can invest your money in the spot market, because whatever the price of bitcoin, as long as you don't sell it, you won't make a loss.
I know that if you invest such money in BTC and look for solid wallet like electrum to stock the BTC for long period of time, you will have every reason to take such decision another time which you can see by yourself what is happening in this bull market that is changing traders story with the huge amount of money they are making from their trading.
If you make spot market where you can stock the money as your choice, nobody will force you against your wish because, if you lost or gain , you Will not going to share the lost or gain with anybody but make your choice wisely with that amount of money.