Don't risk writing down private keys
Yeah, writing down private keys results in a high chance of error. The only thing you should be writing down is your seed phrase(s).
if he already has money for a printer, isn't it better to buy hardware wallet instead of a printer?
If the goal is long term cold storage without making transactions, then a properly created paper wallet is superior to a hardware wallet in terms of security, privacy, and durability/longevity. If the goal is somewhere secure to hold your coins yet still make regular transactions, then a hardware wallet would be better than a paper wallet, but probably still inferior to proper (airgapped, encrypted) cold storage. The main selling point of a hardware wallet is its ease of use for newbies.
the price is about the same if we compare middle-class home printer vs. Trezor one wallet for example.
You don't want a middle-class home printer for making a hardware wallet. You want a cheap dumb printer, without any screens, without any SD card slots, without any WiFi capabilities, without any internal memory. The older the better.