Yes, They guarantee consensus per key ( which is in this case per bucket as they aggregate them).
You won't be able to have atomic operation across bucket neither you can have serialisation of transactions across bucket.
It's a trade-off, my guess is that their use case does not require a consistent view of the overall k/v store.
Indeed, it is a tradeoff, and our solution doesn't require consistency across multiple keys.
More generally, any solution that doesn't require transactions across multiple keys, can use Bizur instead of classical Paxos, and achieve the same benefits (faster recovery from failures, higher concurrency, etc.)
