Referring to the video posted.
Ability to engage safety on Tanfoglio with hammer down is minor design nuisance, more of a fitting issue.
Racking the slide with hammer down and safety on may damage the sear. When hammer is cocked by slide, the sear is raised a little bit - probably depends on the hammer hooks profile. Sear leg is pushed onto safety. It just happens that the model / particular gun you have allows that. I have 4 Tanfoglio-s - both large and small frame, none is happy to cock the hammer with safety on.
CZ mags won't work for lefties who have reversed mag catch. The notches on CZ mags have different offset from the mag top. Even better, old mags or ProMag's, or 26-round CZUB mag may not have a notch for lefties at all.