Many CZs could serve and have served as duty pistols. The OP never specified what model.
The original poster mentioned CZ "Duty" pistols. If he meant service pistols, he shouldn't have "CAPITALIZED" the "D" -- which accounts for the possible confusion. The DUTY is the P-07. (I'm skeptical of any claims about a supply of CZ Duty pistols being offered at a low price; they're simply too new. I suspect he meant "duty" not "Duty.")
On the other hand, not THAT MANY CZs have served as duty pistols. CZ's marketing hype is one thing, reality is another. CZs are widely used around the world, but never in large numbers. (
"Widely used" is not the same as "used by many places in large numbers.") In the past few years a number of small military units have begun adopting them... but the numbers in service are still apparently quite small. (There are probably more Beretta M-9 in service in the U.S. Army than CZs in military or police service everywhere else in the world.)
In many years of tracking CZs on the web and in these discussions, I've yet to hear of any place in the U.S. using CZs as duty weapons, so if the OP is in the US, these are probably imports from overseas. We've seen some, in recent, years come on the market from Europe, imported into the U.S. These were mostly well-used 75s (not 75Bs).
If they're CZ-75Bs, I don't know where they came from. If they're CZ-75s (not "B"s) they've likely got a lot of miles on them! (The Israelis and several South African police forces used them, among others.) The finishes won't be pretty, either, as it'll be enamel or an early version of the polycoat finish. Those finishes weren't particularly durable.
The OP bought pigs in a poke and at least one of them seems a problem for him. The same could have happened with almost any brand.
Re: rear sight getting knocked out of place. That also suggests a pre-B model, as almost every 75B or later CZ I've owned has almost requjired a jack hammer to get the sight loose. Move it back, and use a nail set to PEEN the sight and slide to keep it in place. A single blow is all that's needed.
As for mags dropping loose? Could be bad mag release spring, worn mag release, bad holster, BAD MAGAZINES... Or, as suggested, a holster not designed for the gun.