Well, the one really on the know about the Derby's performance is, of course, you.
I owned the central focusing equivalent of your individual focussing Derby, the 7.5x42 Osprey, for a while and found its coating somewhat obsolete (brightness notably worse than more modern binoculars). My greatest objection however was the narrow angle of view, resulting in the most pronounced tunnel-vision I've experienced in any binocular.
Center sharpness, build quality, looks and handling were really nice but unfortunately, they couldn't compensate for the drawbacks.
Renze