I have been intregued by this idea for a long time. I just got a 9+ and thought I would give it a try. I moved all of my business documents to a google drives and OneDrive.
I am able to put many of my critical apps on my phone and computer, so there is a compatibility there.
For the most part, it is super fast, as fast as my Surface for most office tasks.
I can actually work for a full day without missing my laptop. I can open multiple apps, multiple windows, do email, web etc. I am currently doing this on my Dex.
In general, it works really well. Android apps are not as consistent in their support of keyboard and mouse, so there is a little wierdness sometimes, but it generally works fine.
Many of the Android apps are less full featured, so that is a little annoying.
Many of the Android apps don't leverage the larger screen size as well as they should, but it is ok.
My take away is that DEX itself is really well concieved, and works great. The apps have a little catching up to do.
Can you use it for productivity tasks such as email, google docs etc? Yes! It is basically the same as a PC. Kinda awesome.
Where you get into trouble is doing specialized tasks like web development, photo editing etc.
I could almost do an expense report, but I couldn't get all of the receipt scans concatenated into a single PDFfile without using acrobat on the PC. I will give it a try next time, but I was able to most of the work without a PC.
One con: I can't get it to work with a high-res monitor. I have a 34 inch display, and I would rather see 4k.