I had the onyx one but sold it since I have a pebble color one that is shipping soon that I preordered(bought the onyx on ebay). When I was using the onyx one my only gripe was the screen isnt as smooth as the hibreak pro but it was very responsive! The one thing that bugs me on the hbp is the annoying input latency. The minimal phone also is much brighter and easier to light up compared to the hbp. I also like how the mp has a 3.5mm headphone jack which I ended up using a lot with the apple wired earpods. The keyboard took me a lil to get use to but as I was using it I was getting faster and faster. I feel like physical keyboard is the best for eink unless a device is similar in speed to the dasung 078 eink tablet which was VERY fast, and typing was nice.. I hope the mudita kompakt will have similar speed (I also preordered this eink phone) - I will have to decide between the pebble minimal phone and the mudita when I get them.
Btw there was some bugs when I had the MP which were lines on the screen on anything dark, front light wouldnt fully turn off and keyboard alt key for numbers wouldnt always work but I heard a recent update fixed those issues