Maybe it's been updated since his post, but I experience none of these issues in my testing.
1. Can't use brushes because they are slow and render jaggy polygons instead of the beautiful perfectly smooth brushes of Photoshop - literally can't draw a hand-print looking sketch circle as it looks like a weird digital polygon.
2. I use masks for texturing vector layers, literally cannot ctrl+click to select anything in my file because the texture clipped inside of the layer blocks lower layer selection even though it's completley clipped out of view. Makes it impossible to work on my files without going over to the layers and scrolling hundreds of layers and expanding folders to try to find it. This means I can't use it at all.
3. Try to do dumb little things like turn on one of my color modifying layers and it takes 2 seconds to sit there and wait until it activates instead of a few milliseconds like photoshop.
4. Can't activate my fx layer even though it shows that it IS activated and then others show not activated or something... something completely wrong about this, not even sure what.
5. tried to adjust one of my vector layers couldn't hold alt+hover to adjust the point handles.
6. Trying to type text, takes like 1second per character just to type (photoshop is instant).
7. Can't drag UI sections like Navigator/etc. over to the other panels and can't collapse/uncollapse panels.
8. Can't fill/edit the vector path drawing tool at all I don't think, maybe the UI is just weird but definitely a UX issue or just unusable? Not sure...
I'm not going to bother trying more things, but literally every single thing I tested had a bug or is janky to where it's unusable in a professional context.
I do see 100s of people are working on it now with 10s of thousands of stars on github and it does seem a hair better than my first test, so I'll keep watching the progress, but so far it's just too buggy/glitchy/missing features to work with for me (I have a pretty decent Windows pc - nvida rtx 4080 card, 128gb ram, etc).