I've now compared four different takes on mantra meditation: Patricia Carrington's CSM method, Dr. Herbert Benson's Relaxation Response, the 1 Giant Mind technique, and NSR (Natural Stress Relief). Actually five if I count Russel Simmons' book Success Through Stillness. And I'm happy to report that all of them are basically describing the same thing. The NSR manual might be the hardest to find of these options, but I do recommend seeking it out just to have access to one more pathway.
Between these forms, there are more similarities than there are differences, and when there are differences they are often very subtle. More like flexibilities.
In her book Patricia Carrington points out the differences between her Clinically Standardized Meditation (CSM) and Benson's Relaxation Response, and I wouldn't have even picked up on the divergence if she hadn't pointed it out. Also sometimes the comparison is made in a qualitative way, such as referring to another system as "superficial". I disagree. There is insight to be gained by exploring the different ways in which you can whistle the same melody.
One thing I've concluded is that mantra meditation does not need a brand name. For that reason, I am coining mine In Dipping Ease. That'll be $395, please.
I have also realized that a one syllable mantra helps to disconnect it from breathing. If you are of the opinion that you don't need to coordinate the mantra with your in/out breaths (and this seems to be the prevailing advice), then it may help to hear just one syllable in the mind rather than a two syllable word-sound which can then get caught up in the rhythm of an inhale (so) slash exhale (hum).