Let me see if I kind of understand this.
A lot of these technical descriptions are a wee bit beyond my abilities, yet I thought the reason to want to use the earlier Trezor (Model T with the SD slot but with out the SE) rather than the newer Trezors with the SE is because the SE in the Trezor is not fully open source. My understanding is that Trezor said that they made their new model Trezors (the Safes) with SE "as open source as" they were able to accomplish, yet still the SEs contained in the Safe models end up retaining closed source aspects through the inclusion of the SE, which in some sense could almost completely negate the rest of the open sourced aspects of the Safe models, no?
Anyhow, my understanding is that your (@Coin-Keeper) earlier assertion is that if SD protection is brought into the Model T through the added encryption (not saying that I understand how to do that), then there are the same (or similar) benefits of adding the extra level of security (that would come through the SE), without having the sacrifice of any closed source aspects that come through Trezor's later models using SEs.
The issue of secure elements (SE) in the new Trezor Safe 3/5 doesn’t concern me much. Someone has probably already mentioned this somewhere in this thread, but the general chip that protects the keys remains fully open source. The SE simply adds an extra layer of protection, like a taller wall or a gated community that’s inherently safer than a public housing complex. The code that handles and protects the backup, without allowing the SE to access these secrets, is still open-source. The SE only safeguards this sensitive data without having direct access to it.
Additionally, Trezor has an agreement with the SE manufacturer, OPTIGA, which doesn’t prevent the company from freely disclosing potential vulnerabilities. I’m not entirely sure if this is true, but I hope it never comes to that point.
I am going to go out on a limb here and maybe push your thought process somewhat. I am quite technically aware and I feel that the SD protect feature is every bit as good as secure element ----- EVEN ---- if the SE performs as mfg's would like us to believe they do. I do hope the SE's in Trezor are as good as they tell us they are. I plan on getting a Safe 5 when the prices drop just a bit. So in my conclusion a thief with an SD Protected Trezor T and a SAFE 5 in his booty haul would have basically no better chance to acquire the SEED from either hardware wallet ----- IF the SE performs as indicated. SD Protect is rock solid, proven, and basic mathematics. I am honestly more confident that SD Protect will hold up than the SE because it is new and to me isn't acid tested over time yet. .02
I operate in the linux world so all these programs and advanced features like SD Protect virtually run native in linux. Simple stuff for such a big return in a small time investment.
I own a Trezor Model T and use it occasionally. The fact that it doesn’t have an SE and is vulnerable to PIN or seedphrase extraction doesn’t bother me. The primary purpose of these devices is to protect our wallets against potential online threats. It’s our responsibility to keep the device in a safe place. Moreover, extracting the seedphrase from a Trezor One or Model T requires advanced technical skills and specific lab equipment, which most people don’t possess. If I want to increase security, I can use the encrypted MicroSD card protection linked to the PIN, although I rarely use this feature (I only tried it once to test it and didn’t find much practical use for it, as the passphrase is already sufficient).
Of course, a hardware wallet with a secure element is safer than one without it, but you’ll have to sacrifice some of the open source nature due to the partially or fully closed design of these chips. If we want to have 100% certainty about the security of these SEs, we’ll need to wait for someone to develop a fully open source SE, something Trezor has committed to working on.
The main point is: if someone steals my Trezor (without an SE and without MicroSD card protection), the only thing they’ll be able to extract is the seedphrase. Since I use a passphrase (or multiple), the thief won’t be able to access the "correct" wallet... only the standard blank wallet without a passphrase, not the one I defined with this additional layer of protection (the passphrase).
Therefore, if you have a wallet without an SE but also don’t fully trust these secure elements, my recommendation is: use a passphrase! It’s a mandatory feature for all users who prioritize the security of their funds!
Not sure the metaphor you used is perfect but I get where you intended to go with it. I have examined the encryption from the SD's that I have been using for a few years now. The SEED and PIN are hopelessly encrypted without the SD present. To me, and this is just my .02, that is much better than merely placing a high wall around my house (Trezor).
It's great that you feel good like this, the important thing is to sleep without headaches and worries. Besides, it's a good security practice that few Trezor model T users know about!