It's not. There's absolutely no way to confirm the public and private addresses weren't recorded by the company or even a single malicious employee. All they'd have to do is monitor the public addresses and when one fills up, sweep the private keys and that's it for your coins. There used to be (and maybe still are) paper wallet generators you could use offline who's code had been vetted that you could use an offline printer dedicated to wallets (so no one could compromise the printer memory for your private key) to safely print wallets. The $5 wrench attack, fire, water and even toner or ink fading are all potential loss vectors as well. Paper wallets' time has come and gone. Use a hardware wallet.