What makes this method really universal is that everything happens on the app side, no system files modifications are required whatsoever. The tool basically emulates the behavior of the init.d kernel mechanism : it will detect whenever the device is rebooted and execute the scripts located in /system/etc/init.d.
With this init.d support granting mechanism comes a kernel-sided init.d support detection mechanism, so that your int.d scripts don't get executed twice, which would only make for a longer boot time. Basically, when you run the test, it will generate a little init.d script which creates a file on your sdcard. Then, after you rebooted, it will check if the file that the generated script creates has indeed been created in order to determine if your kernel already has init.d support built-in. If the file was created, it does. If not, it doesn't, as simple as that.
An additionnal functionnality to this app is the ability to manage, edit, delete & run your init.d scripts with the touch of a button.
You can check-out the source code of this application and contribute to it at : https://github.com/Androguide/Universal-init.d