I think that since the PDAs (Personal Digital Assistants) aren't dedicated to cryptocurrencies but rather using them as a pocket computer, it would be therefore more secure. I don't really understand security through, so correct me if I'm wrong.
The usual security issues a cold storage faces is in the process of transferring the unsigned transaction to the cold storage and then the signed transaction back to the live device.
I don't expect the PDA will have a nice and simple QR based implementation like it would be possible with modern devices, hence bad surprises can occur at the transfer of those files (which I also expect to be rather clumsy, hence it will lose all its friendliness compared to HWs). Keep in mind that information has to be sent in both directions for signing.
But maybe I am missing something too...
An old PDA lying somewhere is much less suspicious than a hardware wallet.
I agree to this.
Still, I always tell that's safer to keep on hardware wallet only the funds you expect to use in the rather near future while the HODL funds can stay nicely on any variation of paper wallet/seed/steel/whatever.
And imho this security+convenience mix can render the PDA useless.
However, as I said, somebody may find it as a nice free-time project.