It depends on which one you buy.
I have an early series FEG PJK 9HP, its a true milspec clone. My Dad's new PJK 9HP has a slightly different slide and slide stop (the cuts for the stop are totally different). Truth is the new ones have a much better finish and safety. (I had to replace the tiny gritty safety that was also 40's looking mil-spec to an extended one.) Everything else is the same on them, as far as I can tell without taking a micrometer to them.
FEG also had a nasty habit of naming the same gun by different numbers and using the same numbers for different weapons. The FP-9 is/was an early clone with a ribbed slide.
Mauser made a true mil spec BHP clone. (which someone else suggested was actually made by FEG)
FM full sized guns are parts compatible, the compacts are not, as the slide and the frame are shortened, thus internal springs etc. are a custom item.
The arcus guns, as you can see by the photo vary greatly, you can see the slide stop is distinctly different, as well as the shape of the slide.. who knows about the internals.
Bottom line is to look them over carefully, and know what you are looking for.