My buddy has a couple of the Zenith MP5's and has had nothing but good to say about them. My understanding is, they are the cream of the crop of the clones. The price youre quoting seems pretty good. I think he paid a tad more for his.
The MP5's are great guns and easy to maintain. Keep it cleaned and lubed and youll have no troubles.
When you load the first round you need to either pull the charging handle fully to the rear and release it, or from the lock notch, "slap" it and let it go forward on its own. If you ride the charging handle down to close the bolt, the gun will not cycle properly.
If you want to zero the sight, youll need a proper sight tool. You can try and do it with other tools, but its frustrating and aggravating, and you can damage the sight. If you know someone who has one, it will save you some bucks, as they are pricey, and once set, you wont likely ever use it again.
There are Korean mags available for them at a much more reasonable price and work just as well.
As far as the K version of the MP5, they are just a chopped down version. This is an actual MP5K, the semi auto versions dont have the forward grip, as that would put it in the NFA realm. "Handguns" cant have a forward grip.
I had this HK94 to MP5 conversion up until Obama got in. Should have held on to it as its doubled in price now in the decade since I got rid of it.