I concur with @euro. I think switching to Astra SP's or Perma-Sharps is an improvement over Derby Extras.Good to know, I'll hold myself back and not go too far with my pass against the grain, then.
I've heard a lot of good stuff about Astra and Permasharp, I'll definitely give those a try. I'll also see if Wizamet is available in the Netherlands.
Thanks for the suggestions!
And welcome, @parham! You've come to the right place for advice and guidance. As I am a uniquely average latherer, I shall leave the tips to those who are better than I!