storing a seed phrase with washers has very few benefits unless you think that youir house is going to burn down.
Fire protection is one of the reasons for using washers (washers made of refractory stainless steel - the melting point is higher, than in a fire).
but if you thought that you could just store a separate copy of your seed phrase ON PAPER in a bank deposit box or someplace else.
This is a completely bad decision to store the seed phrase (entirely) in a safe deposit box. The bank (their employees) are people who are strangers to you, but at the same time have access to your safe deposit box. If you store the seed phrase in a safe deposit box, then divide it into parts and in different banks.
if you ever have to travel and bring things with you then you might be screwed if the TSA needs to inspect that strange looking device with a bunch of washers on it that showed up in the x-ray machine because it is metal.
Firstly, washers is not for transportation with you to airports (but for long-term storage in one safe place). To do this, use hardware wallets.
Secondly, what’s stopping you from making seed washers on something other than metal (plastic, fiberglass, and anything else that can’t be detected by x-ray), if you want to carry it with you to different countries?
they might think it is an explosive device or a silencer for a gun or maybe it is got cocaine in it. at the very least, they might take it apart and inspect it more closely and in doing so they will know your seed phrase. then they will ask you what it is. and if you tell them what it is then you just told them how to take all your money.
Under these pretexts they can check the personal belongings of anyone, which makes the question “why carry seed washers with you?” even more relevant.
what someone thinks is a rock solid indestructible way to store their seed phrase could become a serious liability too.
There are no universal solutions to get rid of any problem. Seed washers is not intended to be carried and taken for X-rays at airports. Metal washers is a good and effective way to store seed phrases, but in a secluded place for many years.
Don't take washers with you on travel and everything will be fine.