QC on the first WK models were spotty, and they had some trouble with BCG cracking due on some of the guns, so be careful of this with older used guns that haven't been fired much (anyone that's been fired a lot successfully likely had a properly treated BCG). If using the threaded charging handle BCG, it is advisable to upgrade to newer Kodiak one with the extended frill around where the screw enters the BCG, which helps prevent the handle from snapping, or purchase an upgraded high-strength steel one from SBI. Thread locking the BCG is then advisable, unless you want to tighten it constantly. Alternatively, you can get the BCG that uses the non-screw in bolt handle from Kodiak; the charging handle may cosmetically score your charging handle slot if you don't have the steel upper WK, but it otherwise will not break or fly out of the rifle. The True North Arms WK BCG seems to be the best solution, as it combines its charging handle combines an-anti rotation indexing dowel that inserts into the BCG with a threaded screw, both keeping the handle from loosening in use and preventing it from snapping off. The BCG also has a nice blingy nickel coating. I'm not sure if you can get the BCG without the TNA Enhanced Upper, but if you're not going to wait for the SBI upper, the TNA provides several upgrades over the WK default upper, including a brass piston bushing, ejection slot dust cover (though why they didn't do one for the charing handle slot I don't know) , and integrated shell deflector. The upgrades to the TNA upper provide probable equivalent reliability to the MCR for the WK upper platform.
The MCR has an improved charging handle compared to the default WK uppers; it is secured in a different manner, an I've seen no issues reported of it breaking or fling away. The gas block and other components are more likely to be properly tightened and aligned out of the box for the MCR then for the WK, at least according to reports. Some WKs are put together fine; it seems there is more variability in the QC of the assembly process on the WK then the MCR, and that may well be why people have more issues with the WK, like snapping pistons when the gas block is loose and out of alignment on a more poorly assembled WK.
The group mind consensus of CGN seems to be get an MCR first if possible, as its quality is more consistent then the WK's. Your WK may or may not, be OK. If you cannot get an MCR, get the WK and do a complete stem to stern disassembly (short of removing the barrel), re-assemble with high temperature thread locker on the gas block fasteners, and properly lubricate the firearm. For even more peace of mind with the WK, get TNA to build one for you with your preferred stock, pistol grip, trigger etc with their nicer upper, optionally using their lower that has a straight magwell and beaver-grip tail support, or when you get the firearm home optionally adding a WK specific Spectre LTD Spec 180 lower or SBI Lynx lower. Also optionally if you get TNA to build the upper, you can get them to build it with their rifle length piston op rod and a matching gas port length; this may result in more pleasant shooting impulse, and reduce some of the stress on the firearm associated with the default over-gassed nature of its recoil recovery system.
If you can wait a month or two, SBI will be releasing their own enhanced WK upper, with a DI BCG to follow. Also next month the Sterling RS18 will be released, which combines several upgrades out of the box to the 180 platform for a more premium price. Some CGN members have noted a concern with the backer of the project, as there is some controversy with their history with the firearms community; one would have to research that history and decide whether or not that precludes supporting the backer.
