On the other hand, for that use case, I would argue that mobile apps aren't that bad either. Nowadays, at least on Apple devices, stuff like app passwords (probably also seed of mobile wallets) are stored in a secure element, similar to the one you find in hardware wallets. And you're quite unlikely to lose your phone since it's used every day. Also you usually do encrypted backups and even a single backup is enough to restore the full wallet balance of a mobile wallet in the future.
Mobile apps are far inferior to hardware wallet, in my opinion. Sure, maybe the apps themselves are open source and well designed, and maybe they are encrypted when not in use, but you also need to consider all the other things going on on a mobile device. They can suffer from clipboard malware, just like computers can. There are other apps which can read your files or monitor your keyboard input which could steal your wallet file or any seed phrase you enter. Encrypted backups can be encrypted with insecure passwords, or encrypted in a flawed manner, or leak unencrypted information, or be stored on cloud servers, and so on, all of which can lead to loss of funds.
That's not to say I don't use a mobile wallets. I do, for small daily spending amounts of bitcoin which I can afford to lose. But I would never store the amounts I store on a hardware wallet on a mobile wallet.
Of course, airgapped cold storage would be the next step, hence I recommended to have a look at that signing device, which basically allows one to use the cold-stored, fully offline wallet to sign a transaction from time to time and also aids in the creation of that wallet.
If you have a encrypted airgapped wallet, then you don't need that device. You can sign transactions just fine on your airgapped computer and then move them to an online computer to broadcast them. This device is only really useful when you have paper or other non-digital cold storage and you don't have a safe computer to import them to. It is, after all, just a Raspberry Pi behind the scenes, so it essentially
is just a simplified airgapped computer but without any persistent storage.