I'm now using Android N or 7, I know it's still in Beta but the latest release is stable enough for me. As such Android N has a great hidden feature called, FreeForm Windows. Basically it just puts apps into windows like OSX or well, Windows. Though not all apps work with it yet, like games, most of the ones I need to like; Office HD, Terminal, Inkredible, PDF Tools, etc. do and quite well I like to add. I don't use anything special for my desktop, just a custom launcher by the name of. "Smart Launcher Pro 3", it's quite nice, actually my favorite out of the custom launchers, would even love to have something similiar for iOS as it's put's apps in categories. So the answer to your question is yes, it's a tablet UI, though when I'm attached to the monitor I use that FreeForm Windowed mode so the system act's more like a traditional desktop OS. The guys over at XDA are working on getting Remix OS running for the Pixel C, which I personally cannot wait for. Remix OS is a really cool Android version and that will give you a more desktop experience with a user switchable UI, tablet mode, desktop mode.
Look, I would like to reiterate that I have nothing against the iPad Pro, I love using it for my music as the apps available are nothing short of amazing but for my work Android has it hands down. I know Android is a sour subject around here but Android N is honestly pretty good. It has it's issues like every system and is far from perfect but you would be amazed on how much you can actually do with this OS. I mean I even got Open ID to work for the multi-user feature, it's how I am able to mount my user directory from my firms NAS/internal server as a local folder. In which every app can access the folder directly, quite amazing for a tablet OS to be able to do this. Though if you think about, Android is just Linux. My setup may sound elaborate but it really isn't, all of my solutions I easily found by simply reading forums like this and since it's Android, a fairly opened system, if you thought about it, most likely someone else has as well and has even created a solution for it. Example, Instagram is normally displayed in portrait only on Android, iOS as well, though Android has quite a few solutions that sets every app installed to the orientation of the tablet. I use an app called, "Set Orientation, not an original name I know but it works flawlessly and Instagram actually looks pretty decent in Landscape. I mentioned this because it was one of the issues brought up by a few reviewers when they wrote about the Pixel C. In fact many of the issues that brought up were because the reviewer simply didn't know their way around the system he or she was using, a common problem among reviewers today
There has also been a lot of discussion about the lack of optimized apps for tablets. My personal experience though has been a complete opposite of what has been said though. I have found and installed almost 90% of the productivity apps I was using on the iPad Pro onto the Pixel C. Though yes, apps like ProCreate aren't available but I have found viable alternatives that are more than adequate. Apps like, Infinite Painter, Infintie Design (vector), Sketchbook Pro, MediaBang, Artecture Draw, ArtFlow (one of my favorites), Skedio (another phenomenal app), Paper, Cad Touch Pro (one of the best mobile CAD apps I've used, better than AutoCad 360), Sketch Box, SpaceDraw (the most comprehensive and feature rich 3D modeling app available today for tablets running a mobile OS, a simple must have app and looks great on a 4K monitor), etc. I have all of the Adobe apps, same exact one available for iOS,all of the Microsoft app, etc. Though what really makes the Pixel C special is the stuff under the UI, the terminal.
Since the Pixel C is using Linux GPU drivers and not the traditional Android ones, I can actually use CUDA. As in I can run my CUDA based encoders and boy do they fly. With the Nvidia X1’s GPU has 256 CUDA cores it’s quite worth the endeavor as well as I can encode a media file about 5x faster than a iPad Pro as encoder apps for iOS do not utilized the GPU but the CPU. Maybe we will see encoders based off of Metal in the future but right now there all just simply CPU based. GPU computing is amazing and is something that I am just now getting into.
Also using the app BusyBox, I can install scripting languages like Perl, PHP, Python, etc. and other worthy Linux CLI software, I even have a full LAMP server running for when I need to do some web app dev work on the road. Though I have a little app that shuts these utilities down for when I’m not using them.
Everyone has their own ideas and goals for a computer or tablet needs to meet, the Pixel C just so happened to satisfy many of mine.