Installed on my Pixelbook on 5/7/2019. The key feature that I am interested in this version is the ability to backup and restore Crostini containers.
**Note:** I am starting to see several posts on reddit from people who are having problems with Crostini since the update. One person suggested the release may have been pulled. reddit 
What's included in this release. page
The first time you launch the Terminal you will see a messaging saying that Linux is being upgraded and that the Terminal will launch after it completes.
Unfortunately, something went wrong when I started my second container resulting in a complete meltdown of Crostini. See: Crostini Failure After Chrome OS 74 Upgrade
As reported, the Crostini backup feature is available in this release but it is not enabled by default. I did have to enable the flag chrome://flags/#crostini-backup. page reddit thread
It appears the backup function only works for "default" penguin container as I don't even see an option to back up my second container.
My first test backup was written to the Downloads folder on the Pixelbook, my intent is to run a backup and move the file over to my NAS.
I do notice a performance impact while the backup is running. This appears to be a function best scheduled during off hours.
Because I had to re-build my Crostini container, I have the opportunity to test backup and restore. I installed Krusader and Typora in the new container, then shut the container down and ran a backup. Next I removed the Linux apps in the Chrome OS settings, rebooted, and re-enabled the Linux apps to create a new VM and container. Finally, I ran a restore. I observed the the launcher icons for Krusader and Typora did not appear until I started the container.
I have confirmed that Backup only works for the primary container, additional containers are not backed up. When you remove Linux Apps in Settings it appears the entire VM is removed. I have now successfully backed up and restore the primary (penguin) container several times.
Support for multiple containers appears to be different in this version. I can create a second container launcher icons are not created for GUI apps in a second container. Wiki In Crostini
Created a second container. Ran apt update and apt upgrade. During upgrade observed the following:
Setting up rtkit (0.11-4+deb9u1) ... Job for rtkit-daemon.service failed because the control process exited with error code. See "systemctl status rtkit-daemon.service" and "journalctl -xe" for details. rtkit-daemon.service couldn't start.
At this point I am convinced there is something wrong with the support for multiple containers in Crostini since the upgrade to this version of Chrome OS.