I installed Beta 4 of High Sierra 10.13.5 yesterday. The installation went fine, no problems. I am sure this Beta has all the usual security refinements, but the best feature is the implementation of Messages on iCloud which synchronizes all your messages on all your devices. This was supposed to be implemented in 10.13.4, but did not make it. I tested it out some, it is a really handy feature which I will use all the time.