I absolutely disagree with his explanation and his recommendations. You can check the comments to see that he couldn't really prove his point in that video. Also, I think that you miss the entire point here. I'll stop at that as it's not the topic here...
Problem I see with splitting seed phrases in any other way than good multisig setup, is that you will have single point of failure.
Losing single part of split seed words would mean you will lose all your coins and all other parts would be useless.
I could say similar thing for Shamir Secret Sharing, it also has single point of failure.
Yeah, your house footings even if it was a fire or what not probably aren't going anywhere any time soon, so cementing in concrete is a decent idea. Plus, no one's going to be digging that up while you're there, unless someone pulls some Prison Break esque plan on you, but that's incredibly unlikely.
All they need is metal detector to see if something is hidden inside walls or floor, so I think this could be main negative side of using any metal based seed words backup.
I am not saying someone would scan for seed words with metal detectors, but they could used them to scan for other precious metals, so this this would be biproduct.
Shipping physical, clearly Bitcoin-related products (and other goods, too) is always an area of concern.
Price-wise though, I just checked and their markup is actually not too high, considering the extra work for the milling, tapping and engraving.
It's much less dangerous than buying hardware wallets, since this is just a piece of metal and there is no direct connection with Bitcoin.
You could probably ask them to write on declaration paper it's just a metal plate for home use.