therefore use free money to invest, so we can immediately decide.
It is impossible to invest if you don't have money.
Remember that because most of the investors invested their hard earned money and if you are going to use 'free' money to invest, I don't think that you will strive to grow that money.
It seems that he applying a safe risk management strategy. Invest in bitcoin need braveness, capital, strategy, knowledge and experience. For those who understand how the market works and its pattern then invest huge amount of money in it is not a problem but for those who just learn it from scarcity then his strategy is appropriate because unexperienced bitcoin investors can get too much stress if they invest too much money in it.
In reality there's no way for an individual to invest without using his/her money.
There may be some exception but that's the reality in terms of investing. A safe risk management strategy, there is risk management but you can't put it together with word 'safe'.