When I was looking for one I was about to get a Wacom Mobile Studio. All the reviews I read were very positive and most people preferred it over the iPad because they weren’t stuck in a gated App ecosystem, and could use whichever programs they like (like Blender and so on) or any OS they liked (like Linux), just like at home or in their studio. Since it is a complete portable computer you can do anything with it you would do with you normal PC like gaming for example (read a review of a guy playing The Witcher 3 on the Wacom Studio while commuting). A downside of the Wacom Mobile Studio is that it’s basically a Cintiq strapped to a PC and the Cintiq has some parallax issues (this however doesn’t bothers me much) compared to the iPad.
Unfortunately I can’t give you a first hand review since while evaluating it I came to the conclusion that I rarely do art on the go and do almost all work in my workshop. For mobile I use a simple sketchbook and a pencil. So in the end, I bought a UHD Cintiq. x3
The Wacom Mobile Studio is probably the biggest and most expensive one but it can really be a complete Studio with powerful hardware. I was very happy with Wacom products in the past and would probably buy this. You probably also have to ask yourself, if you need more then just a painting software.