First of all I want to say that the NSR manual is by far the best/practical written meditation instruction I ever saw.
All the books I mentioned in my first message only give a very general overview how mantra meditations work without any practical instructions. These general information were quite like those from the NSR manual.
So the intent of my question was to find out what makes NSR(TM) so special compared to these other mantra meditations?
For example what difference does it make to use the mantra synchronized with breath (this is instructed in some books) to the unsynchronized repetition of the mantra (NSR)?