I wasn't expecting to like this since I'm mostly happy with Windows 8 as it is and don't see the need for stuff like emulating old versions of the start menu, but it's actually pretty sweet. You can set it up so WinStore apps run fullscreen like normal, but with the ability to basically turn the app into a desktop app (and back again) with a simple keystroke or GUI button press, which actually feels fairly quick and natural. This is ideal for me because again I'm happy with the default behavior *most* of the time (on my laptop), but occasionally hit a situation where I want to see something else at the same time and the snap view doesn't show what I'm interested in.
My biggest issue - which tbh is kind of a dealbreaker in terms of my buying this and keeping it installed, but since it's a beta maybe it'll be changed/fixed (or made optional to the extent it's intentional) by release - is that the recent apps thumbnail list on the left is (IMO) basically broken by this. It borks the switching animation (which I find makes the system feel smoother and doesn't slow anything down significantly, plus the non-animation here adds some weird flicker as well), and WinStore apps running in "desktop mode" still appear in the thumbnail list and switch to the app on the desktop, which I find disconcerting.
Basically, what I'd personally prefer is that apps running in "new UI mode" should behave and be treated by the system exactly as WinStore apps are now (so they should suspend/resume, be shown in the thumbnail list, NOT be shown on the taskbar, etc.) and WinStore apps running in "desktop mode" should as much as possible behave and be treated exactly as desktop apps are now (so they should NOT suspend/resume, NOT be shown in the thumbnail list, be shown in the taskbar, etc.). I know some people like the idea of having a unified taskbar but I actually like having apps that suspend/resume be off to the left as it clears up the taskbar for more pinned desktop apps. I also think it makes sense for apps with completely different lifecycle mechanisms to have different UI for managing their lifecycles. If not for this issue I'd definitely pay the $5 for this otherwise very cool mod.