Recs.
Updated
Windows 10 Mobile (previously Windows Phone) is a series of proprietary smartphone and tablet (under 8-inch) operating systems developed by Microsoft.
SpecsUpdate
Pros
Pro Microsoft Office available on the device for free
Windows 10 Mobile / Windows Phone comes with Microsoft Office which is bundled by default inside the system. The newer version of Office uses a similar interface as the desktop counterpart. The usage of the Microsoft Office is free of charge.
Pro Easy synchronization / continuity with Windows 10
Windows 10 Mobile now has the ability to synchronize notifications, calls and SMS to a Windows 10 PC, which allows for continuity between phone and desktop, eg: when a user dismiss's one of their notifications on the desktop, the notification will also be dismissed on their phone as well. In addition, a user can also have the ability to send SMS from their PC through Cortana or the Skype app as well as make a phone call through the Microsoft Phone app in Windows 10.
Pro Conveniently use a mobile device as full PC experience
Windows 10 Mobile comes with Continuum feature where users can use a phone/tablet as a full desktop PC experience when the device is connected to a monitor, keyboard and mouse using a specific dock. The apps used on the Continuum will be the desktop version of the app which is keyboard and mouse friendly rather than smartphone app. This is currently available on selected devices such as Microsoft Lumia 950.
Cons
Con It's connected to Microsoft
Doomed to update, the fate of Windows. By association, you're pretty screwed.