I don’t even think the advice should be using separate device but rather he should be using a cold wallet for the storage of bitcoin, most at times the cost of a very good hardware wallet is even much cheaper than getting extra computer or device except you want to build or set up your own cold storage.
Cold wallets can be recommended many times but remember that it does not automatically save you.
If you want to buy a hardware wallet to use, it's your good start but not enough. You must buy it a right way, and before that you must choose a good hardware wallet for purchase. Additionally, with any wallet, make its backup for wallet recovery later.
[LIST] Open Source Hardware Wallets.[GUIDE] How to buy a Hardware Wallet the right way.Creating a cold storage wallet with Electrum.How to backup a seed phrase.