You are completely taking risk for shifting your ADA to ETH but if you think that's the best choice, do it.
Everything has its own risks, we don't need to worry so much about it. Since ETH is a good coin so far, I think it is no problem to sell ADA for ETH. Every coin has the potential to increase as long as it is not a scam coin. I think it is okay if he already considers everything to hold ETH.
Yes, I just mentioned to emphasize that he's taking risk if he thinks it will be the best for him. I know that Ethereum is a good coin and I hold it as well but someone who's too doubtful with his decision and can't rely to himself sure is taking a risk.
Whether he buy a good or bad coin, as you have said, everything has it. Ethereum is one of the best coin that I have but I also read good reviews about ADA so it's up to him on how he will react to the suggestions here.