Hi, Janek, first and foremost thanks for sharing so much knowledge and time with us. I admire you, enjoy your music and wish you the best.
I've been using the Hanon method following your advice and I find it quite helpful. There are exercises (for instance, ex. 3) that involve playing a lot of ascending and descending fourths. My question is: how do you fret 4ths? do you barre the notes, or use different left hand fingers for each string? I find it difficult to play clean and fast series of 4ths.

Thanks in advance.