I’m a massive fan of their work, as an artist and as a software developer. The interface is simple, but effective and the shortcuts are intuitive and very easy to get used to.
The only major downside is that it only supports painting on one layer. That being said, it’s good practise to work on one layer every now and again, it just required more planning.
My favourite features are the free canvas rotation and that it records the whole process as a video (with support for various codecs). This is incredibly useful for speedpaints and I think I’ll definitely try a speedpaint with this when I have more time.