Tbg, please take the time to read the many reviews for the trimmer. You will find that the trimmer is intended to bevel the entire surface of the edge. Reasons for beveling the edge completely include (1) eliminating surface imperfections on the edge, (2) truing up round of the disc and (3) redirecting the scattered laser light, none of which would be accomplished, or completely accomplished, if only half the edge was beveled.
Lastly, can I point out CD cleaners do not perform any of the functions of the disc trimmer, therefore should not be viewed as replacements for the trimmer?
I rest my case. :-)
~ Cheerio