I had one of the unfortunate early Edwin Jagger's that I believe used Muhle STF and randomly had some very unpleasant scritch. Very unpleasant. I thought it was the knot and avoided it for a long time. Since then, I've re-explored the Muhle XL and it's absolutely fantastic. My go-to favorite synthetic. It's possible that some may have encountered an old Muhle with that random scritchy-ness?This is odd. Having used STF knots for 10+ years and sold many brushes with them, I never felt any scritch/scratch and none of my customers have reported anything like this. It always amazes me how different our perceived feeling of brushes/razors/blades are - it is purely subjective to the individual.