Questoris versus Mechanicum Knights

What is the difference between Questoris Knights and Mechnicum Knights in the Horus Heresy? I've been asked this question a small number of times, but thought I would save it up until I reviewed the Knights out of Liber Mechanicum to make a quick summary.Background.In terms of the lore, the difference is remarkably straight forward. The Questoris Knights have sworn loyalty to the Imperium of