Those bags are useless, and will provide zero protection.
They provide zero protection, but they are not useless.
Take the situation where you have a seed phrase backed up in one location and a passphrase backed up in another. If you notice that your seed phrase's tamper evident bag/seal/whatever has been broken, then you will know that an attacker has your seed phrase and may be attempting to brute force your passphrase, and you will move your coins immediately to a new wallet. Without a tamper evident bag, you would not have this knowledge. You will also now know that that particular back up location is not secure and you will stop using it, information you wouldn't otherwise have.
No single back up I have is enough to steal any coins from me, but I definitely still want to know if any single back up has been accessed by someone who isn't me.
You ultimately need to store your entire seed, including any passphrase in (an) offsite location(s). Otherwise, you risk losing access to your coin.
If your security model includes storing portions of your seed in various offsite locations, a tamper-evident bag may provide
minimal additional security. Like I mentioned above, these bags are typically transparent, so an adversary will likely not need to actually open the bag in order to see what is inside. It is also probably trivial to do things such as fold/unfold items inside the bag, as well as open things such as an envelope.
I am also not sure how often most people access their off-site backup location. I think for a lot of people, this is fairly uncommon, especially if the location is far from their home.
The purpose of a tamper-evident bag is really to provide assurances that the content inside the bag has not
changed. This is really not an important question when restoring from a backup.
Those bags are useless, and will provide zero protection.
They are not meant to offer any protection, they should just to tell you if the bag was opened or not, something like sealed envelope, when you break the seal you know that content inside was compromised.
As I mentioned above, it really tells you fi the contents inside a bag have
changed.
I don't know if anyone is familiar with this, but I found one interesting project called entropy seal for tamper-evident packaging, it is a jar with particles for storing any sensitive physical goods.
I am not sure if they are selling it yet but it is interesting concept, one thing I don't like is that some phone app must be used for capturing and comparing image,
so I wonder what happens if app is dead or not supported in new phone...
https://www.entropyseal.com/Pretty cool concept. Obviously, if your entire seed is compromised, this will not do much good.