If I give someone some money, I get some food, or a house, in return. I don't think it is an illusion as I am sitting here in my house (that I paid for) using my desktop (that I paid for) and will soon be eating a meal (that I paid for).
On the other hand there are many websites inviting you to 'buy bitcoins and make a fortune' but they never tell you who will be paying for your 'profits'. Clearly most of these are scams, they take your money and vanish. If you had bought a lot of bitcoins when it was new you would today be very rich but as the value has gone up and down recently I think most people are losers. The only winners bought that currency when it first started, so we are all too late now.
Money has no inherent value.. it is based solely on debt, criminals printi it out of thin air... nothing backs it up... there is no difference in cryptos ... just a series of 1's and 0's in a computer .... just because people accept it for an "agreed" value, does not mean it HAS value... it is an agreement... agreements are in the mind and sometimes written on paper... still, they do not exist in nature