Crypto currency have a cost, to mine then you need great processing power, a good processor and graphics card
You “pay” for the crypto currency you gain through use of electricity and your PC, especially the graphics card wears out
Crypto currencies have caused a surge in demands for high quality graphics cards
So there is a price to pay. You do “invest” through time, effort and processing power and hardware (like graphics cards)
The number of bit coins, or other crypto currencies, is finite. This allows demand-and-supply, ie basic economics, to decide the price
I think crypto currencies may end up being very valuable and may destabilise the normal currency markets
If you can get involved, without spending too much on PC hardware, it may be worth it. Though I think, looking at graphics card prices now, that that ship has sailed
In a way it’s not unlike a pyramid scheme, in that works out most for the early adopters
There is a new set of crypto currencies developed for mobiles, much more accessible to ordinary people. All you need to do is click a button once a day
Look it up if you like (don’t want to advertise any particular one)
IMO it’s worth getting involved