It's safe as long as it doesn't experience a decline, but if there is a decline like now, then it's as if security doesn't exist and some people panic so they let go of assets like ETH and BNB that they already have.
I don't understand about the meaning of "safe" and how to define it in a fluctuating market because every price is as unpredictable and full of risk as the drastic price drop on Coinmarketcap yesterday. ETH and BNB coins are the top coins and why would you doubt the safety of investing in them, if emotionally you cannot accept the risk of loss due to market factors then wait for the right moment to buy them.