Is it really the best way to invest your money?
Because of the way Bitcoin generates value or becomes more expensive, it could potentially lose all its value and became worthless.
Who assures you that this will not happen?
This depends on your goal but the only person that can answer that is yourself.
If you have the means of investing for long-term, then I highly recommend so. There are lots of people (including myself) have profited in investing into cryptocurrencies (BTC to be specific). It has an inflationary nature where its value may increase substantially in the following years. But again, this is subject to certain risks that are associated with it.
If I where you, I suggest watching videos about BTC as there are tons of materials available in the internet. Upon learning everything, you decide if you think it is best investing.