Bear with a few of the real time hesitations - Steve has recorded this in real time, so it's as if you're in the room with him. No tricks, just Continuum running on Windows 10 Mobile hooked up (effectively) to the largest display you've ever seen:
Steve's colleague's full, exhaustive (and overly technical, you have been warned!) review of the 950 XL is also online, here, albeit translated from the original German. Here's their verdict:
The long wait for a new flagship smartphone from Microsoft was worth it. The Lumia 950 XL is a great high-end product, which does not make any mistakes in respect of the technology. Besides a fast SoC, you get sufficient storage, which can also be expanded. The camera can convince as well and takes both great pictures and videos. Microsoft implements a new USB Type-C port that even supports the USB 3.1 standard, which is currently unique in this segment.
Just this port is the key for Continuum, which can be a real benefit and creates new possibilities. Microsoft also throws in one year Office 365 as well as a Display Dock if you get the smartphone now. Windows Hello is a simple and reliable authentication method and is well integrated into the system.
The Lumia 950 XL is a smartphone with good specs and great features, which can be used as a PC replacement thanks to Continuum.
The biggest issue of the smartphone from the software giant is actually the software. Both the idea and the user interface of Windows 10 Mobile are just great, but the operating system unfortunately does not appear to be quite ready yet. The store also lacks a lot of apps, which is actually a familiar problem for the mobile versions of Windows. The voice quality could also be better for a high-end device in this price range.
If you are looking for a great smartphone with Windows 10, the Lumia 950 XL is definitely a good choice and there aren't any serious alternatives.