Why do you say that they don't hold, exactly? We take our consistency guarantees, and correctness more generally, deadly serious. I think it's fair to say that we did quite well on Aphyr's review; he's found some quite obscure issues that were quickly fixed. More details here: https://www.cockroachlabs.com/blog/cockroachdb-beta-passes-j...
That is empty talk, ie advertising.
In a distributed database, as is the state of the art, you sacrifice one of: availability, consistency, performance.
This is true for every db, be it Spanner, or MongoDb.
Best to document what exactly was sacrificed. Just claiming that you "take it seriously" means nothing. BTW good luck :)