A topic that has come up in several lessons recently is that of learning B-flat horn alternate fingerings in the middle register where I would at least normally us the F horn. It is important for horn players to learn these fingerings in this range, which is one reason I philosophically prefer as a horn teacher B-flat marching horns to F mellophones–those students will learn those fingerings well. In short, though, every advanced horn player needs to knuckle down and learn these at some point.
The late Louis Stout, of Holton and University of Michigan fame, was a big advocate of B-flat horn fingerings and had a method he used to teach them. Basically what I have been told is that if a student did not know them well enough he would take all the F horn slides off their horn, put them in a drawer in his desk, and they would just have to use only B-flat horn fingerings until they knew them well enough to get the F horn slides back.
I don’t think any horn teacher would do this today (I would not, anyway!) but it does communicate the importance of getting these fingerings worked out.
Louis Stout was a fan of the single B-flat. This horn is one he helped a student purchase, a Holton single B-flat with an F extension. Just the horn for Mozart if you studied with Prof. Stout.