Just finished playing through both books of the good old opus 6 "low horn" etudes, using the Gumpert/Frehse edition published by Carl Fischer. I actually quite enjoyed going back over these after really only using them as a teaching resource for the last couple of years (AMEB Grades 5 through 7, List A).....It is somewhat annoying to realise that I still find several of the same exercises a real challenge even now though!