You don’t need >100$ specialized plate to back up your seed phrase.
Dog tag and center punch is affordable, sleek and simple! 
Discussion
Good idea but you DO NOT want to wear your seed words around your neck!
Oh and dog tags are very easy to hide 👍
What if I use a custom codex I myself only know to encode it first?
Well I guess it depends on how easy/difficult it is to break/brute force.
☝️
Definitely crackable, but not easy or practical. So first you should subdue me, steal the plates, and have the know how to crack the code. You should also know what do those symbols hide. Would that be worth for the satoshis of a pleb like me? 😊My guess is most people that would be intetested in stealing like half BTC lacks the know how I described. Ultimately however, every approach has a blind spot.
I would advise against it 😉