I've just ordered what looks like an identical Edwin Jagger brush from The English Shaving Company brings you an extensive range of handmade Edwin Jagger razors, shaving brushes, shaving accessories, shaving creams and aftershaves where it says it has a 21mm knot.

I already have an onyx-handled super badger brush which I love "Shogun" Luxury Onyx Super Badger Shaving Brush :: Shaving Brushes :: Shaving Shack It measures 24mm as it comes out of the handle, I don't know if that is defined as the true knot size though.

My super badger is lovely and soft, and using it to apply warm lather is very luxurious, but I do wonder how badly I'm missing out on the scrubby effect from a stiffer brush, which is why I have ordered the C&E/EJ best badger brush to try.

The main advantage of a larger knot is more hairs=more water and more lather is held in the brush. It also makes the brush firmer, but you have to factor in hair length, packing density and hair type in to that equation.

Best badger is relatively stiff, so you can get away with having a smaller knot size.
My super badger is quite floppy despite the large knot size. But wow it feels nice.