1. The opacity and complete coverage was higher for the period brushes. Looking at the paint done by a modern brush there is a fading on the edges. Not so with the period brush.
2. When you made a brush stroke, there was some blobbing (technical term) and uneven lines or breaks. I am not sure if this is the fault of the brush or the artist, because this is the first time that I am taking these out for a spin.
I did feel that the ability to have such a large amount of paint and a very long tip made for some interesting flow as seen by the Z and A at the bottom.
Action plan: period pigments with period brush vs period pigments with modern brush on velum and paper. A much larger image is below so hopefully you can see some of the details.