I have six (6) ZKK series rifles:
Two (2) ZKK 601 rifles in .223 and .243 both with pop-up aperture sights and both currently being rebuilt and customised,
One (1) ZKK 600 in 7x57 with pop-up aperture sight,
Three (3) ZKK602 rifles in .375, .404 and .458 Lott (the last two are conversions and not original calibres) but my 602s do not have the pop-up aperture sight as 602s with the pop-up aperture seem to be less common than they are in the 600 and 601 rifles. The pop-up aperture does conflict with the express sights, so maybe that is why they are less common.
Needless to say, I love the ZKK series of rifles, both with and without the pop-up aperture sights, and I am always looking for more of them.
Out of the box they can be a little rough but it does not take much work to clean them up and smooth out the action. Spend a little money and restock and you end up with a great rifle that is 'streets in front' of most modern rifles. But, as much as I love the ZKKs, I have never been fond of the original safety.
Accordingly, I have been changing the safeties on my ZKK series rifles to the three-positional bolt-shroud safeties like the Winchester Model 70 safeties - which I believe is the best safety system available. Over the years, the kits for these three position safeties have been available from a number of sources but I think that the only source, at this time, is Ed Lapour Gunsmithing (see
http://edlapourgunsmithing.com/3-position-safeties/ ). These turn the ZKK series of rifles into something even better than the great rifles that they are. The only problem with the Ed Lapour safeties is that, with the recent hassles with exporting gun parts from the USA, Ed will no longer export these safeties. I find this frustrating because other companies such as NECG have been approved to export three position safeties for Mauser 98s, so I do not understand why Ed Lapour won't export his safety kits. It just means that us foreigners have to think up more imaginative ways to get our hands on these safety kits.
I will try and post some pics of my ZKKs with the 3 position safeties over the next few days, if anyone is interested?