Changes include ( comments in Italics are my own):

Server Install Fix: "When you install the App-V Server management database (DB) by using SQL scripts, an SQL error is reported. The workaround that was first documented in App-V 5.0 Service Pack 3 (SP3) is now incorporated into the SQL scripts to eliminate this error." This fix addresses only the  initial installation of the App-V server system where the external SQL scripts are used to create the database.  It has no impact to existing implementations and would only be useful in new installations of the Management Server database where the database is on an external server.

Server Fie: "The App-V 5.1 server update installer now links to the correct content (Privacy Policy and the "App-V 5.1" page)". This fix is applied to the Management Server, I am unsure what the issue was but it sounds like a minor link in the installer itself that nobody uses..

Server Fix: "On the Server Management console, applying an action to a filtered subset of packages actually applies the action to all packages.".  This fix is applied to the Management Server. It only affects the management console and level of importance depends on how many packages you have., as you don't use the filtering feature until you get to maybe 50 packages..

Fixes "Group-specific functionality is incorrectly made available to other groups if the Optional feature is used". This is a probably a client fix, but they didn't provide enough detail to be sure.. 

Fixes "After the first-time sync of a Connection Group (CG) on the device, newly added packages to the CG are not enabled".  Appears to be a client side fix (both desktop and RDS clients), and I am guessing only when the App-V server is used.

Client Fix: "Using Dynamic Virtualization, file handles are not closed when a shell extension is unloaded. This issue can cause Explorer.exe to keep DLL file handles after a shell extension unloads them. This can block upgrade of the shell extension".  This is a client side fix (both desktop and RDS clients).  It is probably far more important to the RDS use case, but would not likely solve the need to have a maintenance window to get everyone logged off to clear out all pending updates.

Changes claimed to be included ( comments in Italics are my own):

"The FullVFSWriteMode tag in a Sequencer template is ignored." As there appears to be no sequencer release in the hotfix, I call bullshit. Update:  It seems that this fix only affects command line sequencing and is not included in the released files.  If you ask your ever-friendly CSS representative nicely it might be available as a privite fix.

When you go to request the hotfix, they email you a link to download.  On step 1 you must click the "show hotfixes for all platforms and launguages (3)" link to see the App-V hotfix.  Otherwise you'll only end up with the MBAM fix.

Note: Windows 10 version 1607 and above, and Server 2016 and above, clients do not install these hotfixes as standalone installers any more.  The fixes would be applied to, and delivered by, operating system updates delivered via normal channels (e.g. "Windows Update").  Microsoft tells us that fixes should generally appear first in the 10/2016 branches before releasing the 5.1 branch; While I'm sure this is the case for security fixes, it is not clear that non-security client fixes (such as the last three in this list) have been released at this time.  Additional file changes may be involved with this App-V update.

NOTE:  App-V Hotfixes always include prior fixes on the same release.  In other words, you only need to apply the latest hotfix (5.1 HF7 in this case) and it includes other prior hotfices (5.1 HF1 through HF26 in this case).