Here's the rub: You're running Windows 10 Mobile apps, not real Windows apps. Not only are there very few such apps -- the only browser, for example, is Microsoft's Edge -- but the ones that exist can't do what real Windows desktop apps can do.
Look no further than Microsoft's own Office apps. At first, you'll be impressed that, when you run Word or Excel from that docked Elite x3, you get a desktoplike full screen. Sure, the Windows 10 Start menu is replaced by the smartphone's home screen, but that's fine. Excel, Word, PowerPoint, Outlook, and Edge all look like the real thing.
When running apps on an external display from the Elite x3, you get the Windows 10 Mobile app -- not the full Windows 10 app -- and the Start menu is replaced with the Windows 10 Mobile Start (home) screen.
Except they're not the real thing. You soon realize that you're not running the Windows desktop you expect and probably need. Office for Windows Mobile is much, much less capable than the Windows 10 Office version, much less capable than the MacOS Office version, and even less capable than the iPad Office version. (It's about a match to the native Office for Android version and to the Office Online browser versions.) The same holds true for Outlook, where the functionality suffers from the same limitations Microsoft has imposed on all platforms but standard Windows.
Thus, your Elite x3 lets you touch up and revise Office documents, but that's about it. Forget about serious document creation and formatting -- no style creation, for example. It's simpler to stick with a laptop if you need full Office on the go or to use iOS or Android mobile devices (and get access to their much larger business app libraries).
Did I mention how very few native business apps are available for Windows Mobile?
You'll also quickly realize you don't get the full Windows capabilities such as taskbar widgets. You are running Windows Mobile, not Windows. This is not HP's fault, but Microsoft's. Microsoft has not ported the full Windows to mobile devices running on the ubiquitous ARM processor, merely a subset. HP can't fix that; it can only decide if it should build products on what Microsoft has made available.
When in display-control mode, the Elite x3's screen becomes a trackpad for the external display.
Yes, the Elite x3's ability to show a full-screen app on an external display is cool, as is its ability to provide access to keyboards and mice. But that cool factor is not worth running a crippled subset of Windows apps.
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