MacOS – Mac OSX installer is disabled or not accessable

The update did not work for me, as I had already run it. It broke after the update. I still had the problem. In Finder, I could see that the file extension icon was not the gold/tan box icon that goes with Installer. There are two ways to do this. 1) In Finder, right-click, or get to the property window, and "Open With" and navigate to /System/Library/CoreServices/Installer.app. There is a checkbox to always open with this app. -or- 2) Open Installer itself and drag the mpkg file into it. Run the installer.

Both of these should run, and also change the mpkg icon in your Finder.

"so what would be the 'correct' way to provide it to you, OS X users next to main software?"

Either. If the installer is relatively large in size, I've found that it's contained in a dmg versus a pkg, however. Why?

A .dmg package is seen as a single file rather than a folder of files like a .pkg package....The advantage a .dmg package has is that larger files may copy much more quickly to your distribution points than .pkg packages.

In my opinion (again, from the perspective of the OS X user), dmgs are intuitively easier to use: mount > drag > drop.