I really like the ST-1, Jon. I have one of those knots in a Highlander brush:It’s a Oumo ST-1 Super Fiber, never tried it so is a risk.
Post in thread 'Highlander brushes' https://www.theshavingroom.co.uk/community/threads/highlander-brushes.57249/post-945403
I'd be happy to have more ST-1 brushes (if there was space in the den!)