You may be right to question this. There has been a lot of disagreement about whether the M57 safety is an importer add-on or factory safety. I don't know whether the safety was included in pistols as issued to the Yugoslavian military, although I believe the M57 safeties are appropriately considered factory safeties.
I know the early M57s had no safety; that can be verified from photos as well as by people who own them. As well, I own an early M57 (probably 1957 or 1958, based on the 4-digit serial number without a letter prefix) with a safety that was clearly added later. So that makes it an add-on of some sort, but on the another hand, in a description by Slobodan Krstic of the evolution from the M57 to the M88A pistols, including the evolution of safeties, the earliest safety described is precisely the system used on the M57 -- a "simple mechanical safety, fitted on left-hand side of frame above the grip, that locks striker and slide." This is the safety used on the M67, the M57 redesigned for 9mm. This safety was later replaced by a frame-mounted safety locking the slide and firing pin, used on later M67s and some M70s (a version of the M67). This safety was replaced by a slide-mounted safety locking the slide and firing pin, used on the M88A but not the M88 (both based on the M57). The CZ99 comes with a frame-mounted safety or, optionally, a slide-mounted safety.
Again, the safety found on the M57 is the earliest safety design Krstic describes.
So, is the M57 safety an add-on for importation or is it a design integrated into the pistol? Well, it is clearly an add-on in that it was not part of the original design. On the other hand, the safety was part of the design of pistols based on the M57, and at some point was added to M57s.
Compare this to the safety included on the various Tokarev clones. For example, on my Romanian TTC the safety is not only crudely made but hinders routine disassembly and assembly, making it take much longer to field strip than my M57, mostly because the TTC (add-on) safety makes it very difficult to remove and reinstall the slide retaining pin, which should be a simple procedure. This safety is an afterthought, and could have used more thought. (I may end up removing and machining it to both clean up the crude workmanship and, more importantly, make it easier to field strip the pistol.)
Finally, I'm not sure I'd put too much weight on the Zastava website. In the civilian pistol section of the website -- the only section with pistols -- Zastava has M70s with and without safeties, and describes different safeties for different models of the CZ99. Clearly, Zastava is pretty flexible about installing safeties on civilian pistols.
Originally Posted by AimHigh
Gun-Shy: You said: " The first models had no safety, but later a safety was integrated into the M57 design (so it is not an add-on for importation, as with standard Tokarevs)." The Zastava web site only shows the right side of the M57 but it does show the left side of the M57 LUX. No safety is visable. I wouldn't think they would market a version with a safey and not emphasize it. They do show the safety on the M70 "Exclusive" though. No disrespect intended, but where did you get your info? Just curious. -AimHigh