I have a few, and used one for myself. It is getting better, but it is not the standard of Muehle STF knots.
The Oumo fibers are thicker than the Muehle and much thicker than the Wald. It is much closer to a Muehle STF than a Wald knot.
It comes in two shapes, a bulb, which I would call a rounded fan and a fan.
My brush is the bulb, and I set it at 53/54 mm, a tad higher than they say, but to be honest, it would be better at 55/56 mm, the height I set my STF mostly.
It does not splay as easy as the STF knot. Also, the size is larger than the nominal size, the 25 mm knots need a 27 mm hole, while the 25 mm STF knot needs a 25 mm hole.
One picture shows the brush with the Oumo bulb knot, the other a Muehle 25 mm STF and this brush side by side. As one can see, the Muehle STF is more rounded.
I would love to show the two after the single brush, but whatever I do the pix of the two always shows up on top.