f/2.8: It’s pretty soft with a little coma and chromatic aberration. There is quite a bit of spherical aberration which lowers the contrast quite a bit.
f/3.5: Sharpens up with a tiny bit more contrast and a lot less spherical aberration.
f/4: Still very soft with low contrast and only a tiny amount of spherical aberration. The chromatic aberration just won’t go away.
f/8: Even at f/8 it’s still not very sharp at all and has very low contrast.
A little bit of vignette at f/2.8 which starts to clear at f/3.5 and is almost gone at f/4.
The blur is quite harsh and distracting and would not make a good portrait lens.
The lens has a lower level of pincushion distortion but nothing amazing.