i think is Bitcoin is safe in my opinion as compare to paper money because no one is stolen your money, you can purchase goods in safe mode
If keeping it safe from being seen by anyone, it is safe, but how long? we never know, bitcoin price moves very fast. I think it should be half fiat and half bitcoin if he want to keep, who knows what the price of bitcoin maybe. and might fall, so its better to be wife, put half in wallet and half in fiat.
If the one million users today have half bitcoin and half fiat, the bitcoin price will be through the roof. I think we have 1% in bitcoin and 99% in fiat.