The team from codl sent me some plates to test. The kit consists of three 304 stainless steel plates, a punch and instructions.
The design uses an innovative encoding system to allow a BIP39 seed word to be stored per column. Each cell is divided into four triangular sections. The first letter is marked in the top section, the second on the right, third on the bottom and the fourth on the left. The first 4 letters of each word in the BIP39 wordlist are unique, so as with the seedmint
For example, if the first word was LANGuage the letters would be encoded as shown below. If a mistake is made you put a second mark in the erronous section.
In this kit there are 3 plates. Each has 16 words so two plates are needed to construct the full 24 word backup.
4 marks per word x 16 words per plate x 3 plates = 192 marks
It took me about 20 seconds per word, which would be 16 minutes to mark all three plates. Adding in the time to read the instructions and take greater care it's probably an hour long process.
The kit comes with a punch, but given I have an automatic center punch I opted to use it.
The plate could then be stored somewhere safe. An opaque spray coat turns the plate into a nondescript metal coverplate which could be installed surreptitiously almost anywhere out of the way.
When the time comes to read the plate a once over with sandpaper restores the plate back to it's original state.
In general these plates are expensive in comparison to a stack of washers and a 3d printed jig (or a borrowed metal jig). If you want to make backups of many seeds it will get expensive using single use products.
That said, BIP85 makes it possible to derive any number of wallets from one seed, so it is likely that in the future one seed will be enough. If you want to back up a single 24 word seed this product is a good choice.
The plates are high quality, the markings are robust and the compact encoding system is clever and quick to use.There are also no moving parts to break unlike many other seed backup systems.
It is also easy to make a mistake. Once you have punched a few letters the system becomes familiar, but until that point it is reasonably likely you'll make an error. I suggest that the instructions include a 1:1 scale printout of a plate so that you can practice marking with a pen first. Once you have completed one side (12 words) I think the chance of an error will have substantially decreased.
Update: The codl team now include an orange permanent marker to premark. This will greatly help with reducing errors. Image of the updated design shown below followed by links to the products.