Hi Luigi,
The caveat with these features is that Couchbase 4.0 only provides per-document atomicity. So there is no per-statement atomicity for multi-document mutations in 4.0. You can use them provided that your application can handle corner cases and error conditions, and provided you understand that Couchbase may or may not provide official support in 4.0. We want to provide full information to our users so that you all make informed decisions.
Thanks,
Gerald