Does the 4.4.1 update improve 3rd-party camera apps or are the enhancements just to the stock camera app? The new minor update to Kit Kat is apparently all about improvements to the camera on the Nexus 5. The official Nexus G+ page says:


  It improves the camera with faster focusing, especially in low light, faster white balancing, for truer colors, the ability to pinch-zoom the viewfinder in HDR+ mode and less shutter lag. 


Will I see these improvements when I use a third-party camera app, or do they only affect the official camera app that Google ships with the OS?
Updates of this kind are usually for the camera as a whole and not just app centered. For a detailed analysis I suggest you read this. The update as a whole brought changes to the API the way the auto focus, White balance, etc in pictures taken as a whole. You will notice changes(for the better) in pictures taken from a 3rd party app too.