AprilSpring

Pros:
MSI had an installation success rate of ~85% (and we have many requests to our tech support team for v1 install failures). MSIX promises a 99.9% success rate.  MSI requires admin privileges to install. MSIX installs per-user, but files are deduplicated so that disk space isn't wasted. MSI apps are not sandboxed from other applications, meaning other applications can break those apps (we have seen this with several third-party apps in the past). MSIX apps are sandboxed to prevent this. MSI updates require a manual download of the full ~550mb installer which must be manually installed. MSIX can perform in-app delta updates which are smaller and faster. MSI updates can only be performed one at a time. MSIX can update all three apps simultaneously. MSI cannot guarantee that an uninstall will leave your machine in the exact state prior to install. MSIX installs are segregated and don't rely on the registry or special filesystem locations meaning an uninstall always leaves you in a clean state. Installation and app data paths are cleaned on uninstall. MSI apps cannot integrate with Microsoft Photos app to provide "Edit In..." style features. MSIX can. MSI does not require a digital signature. MSIX does (this means any MSIX that appears to be from Serif, will be guaranteed to be from us and only us). Cons:
MSI can allow the user to change the installation directory. MSIX can move installed apps to different drives, but it cannot choose a specific directory (due to the sandbox). See below:

  MSI can allow an option to install a desktop shortcut. MSIX doesn't provide this as an option, but you can pin the apps to either the Start Menu or the Taskbar. There is also the secret Shell:AppsFolder location in Explorer that allows you to right-click or drag the icon to your Desktop for a shortcut as a workaround if you need it.
 
  MSI has easy discovery of undocumented app locations for launching from a third-party. MSIX hides the install location due to the sandbox, but we use App Execution Alias to enable this scenario. You can find the aliases in the following location: C:\Users\username\AppData\Local\Microsoft\WindowsApps\AffinityDesigner2.exe
C:\Users\username\AppData\Local\Microsoft\WindowsApps\AffinityPhoto2.exe
C:\Users\username\AppData\Local\Microsoft\WindowsApps\AffinityPublisher2.exe
Remembering to replace username with your Windows username. Also, those paths are already in your %PATH% variable so you can often launch them without even specifying the full path, e.g. just AffinityPhoto2.exe. There are bugs in some third-party applications with the App Execution Alias , and the next post includes aflaunch.exe as a work around if you need that instead. 

Thank you. You don't know how long I fought this - the answer is so simple. I appreciate all your thoughts, help, and time.