All stainless steel plates with bolts I saw in his testing tended up performing poorly compared to regular single plate without bolts.
Most other designs which include bolts or screws are designs which utilize the "tiles in a holder" type design, which I agree perform very poorly as even a small amount of warping or movement and all the tiles fall out. This design doesn't feature the same drawbacks, and if the screw or bolts loosen up a little here then no data is lost.
The tiles-style backups are not as durable as I would like. They tend to be quite popular but I can't really recommend any. In our solution, the bolts are quite big and strong, and even if they broke, your data is still fine, just like you said. The thick plates where your seed is marked are not going anywhere, these are monolithic.
On the other hand, if I make mistake with Coinplate I will have to throw it away, order new one and wait for shipping.
I don't think so. If you mark the wrong letter it would be pretty trivial to hammer in a few more marks to obscure that letter to signal you made a mistake and instead mark the correct one. You would have to make a large number of mistakes for it to be completely unusable and require an entirely new device.
That's exactly what we recommend in our instruction manuals, unless you make more than 3 mistakes on each letter you should be fine. Still, we include a marker pen so you can test mark your seed first, double or triple check and after that make some dents in the metal.