Great features! Although, I've been using Application Guard in Microsoft 365 Apps for a while now and experience many reliability issues. Here's a few examples:
1. The first "untrusted" document gets opened in Application Guard-Microsoft 365 Apps and works just fine. But when I try to open a second document, an Excel splash screen with message "To keep you safe, we're opening in Application Guard" just keeps hanging there forever without actually opening the document.
2. After a short while the "Microsoft 365 Apps protected by Application Guard" window becomes unresponsive and either crashes or becomes unresponsive and can only be closed using task manager.
My PC has Windows 20H2, i7 CPU, 16GB RAM, SSD, etc.
Although the idea is cool, but in my experience it is still quite far from being production ready.