The watch is aesthetically great, but I'm suspect of any (expensive, say >= USD $4k) brand that will not guarantee an accuracy range. It doesn't have to be COSC or METAS, although those will do nicely. For example Oris guarantees some watches at +3/-5, or Rolex +2/-2, or even Seiko promising +15/-20.
If they can't state that owners can expect +/- something, they are in essence saying that when you get your new watch home and it's losing 20 seconds a day... oh well, that's on you, chump.
For several thousand dollars, you should be able to send it back to the manufacturer for (free) regulation to a promised range - and if they can't do it - a full refund (unless it is obviously damaged by the owner).
My guess is that great brands like IWC or Cartier don't claim any level of accuracy because they don't want to incur the cost of supporting their timepieces. That approach - again, in my opinion - makes them lesser watchmakers, and I'll still be scoffing at $12k for a steel watch, regardless of who made the movement.