I always go by the old school method of writing on paper but to answer the question QR code should convert the format in completely offline so if someone using an air-gapped device then it's same level of secured as writing on paper, but if the device can expose to internet while reading or even after we done we can't say for sure that our seed is completely safe with us.
With particular emphasis on safe,
Just how safe can this method to wallet key security be?
The idea about keys to a wallet of this nature is how it could be completely secure and then, having it in a QR code formate might be a very simple means but, its just a scan away from being hacked.
Meanwhile, most the mobile devices these days don't need an icon to be clicked for searching out the program behind a code. Just a flash of the device camera and the code is linked.
Now, does this automatically suggest you a wallet for download for you or itould just error out if you aren't scanning from a specific wallet.
It's the user's responsibility to keep the seeds that are converted into QR codes in a secured environment where no one can access them except you and just same as writing and storing the seed words, the only purpose of converting them into QR codes is convenient which I don't practice as said.
If you are scanning QR for a specific purpose like scanning to make a payment and the app doesn't recognize will show it's error but just a split second is enough to read the QR code data by the reader so if you are hanging the converted seed in a place where someone can snap then you are inviting people to steal what you have.
