If you want the utmost clarity from your CDs

I would think if it had any merit at all, the manufactures would have thought of it and maybe included something similar in the box, or redesigned the cd tray. I'd have to agree with a few others, that it very well may throw off the laser reading. To me, my cd's sound fine played in my machine as is. It is more a thing of mastering than anything else. Kudos to the willingness to try it, just not for me, nor is the green pen thing. 

All I can say is that on my set it brought everything better into focus.

Great, now I need 180g CDs?

Try cleaning them with products such as ReVeel/ReleeS that come in sachets/spray.

De-magnetising and removing static from CD's works, by either method, before inserting the CD into a transport, or by mats / discs used on top of the CD during replay. 

It is a very cost-effective means of "improving" sound, especially on CD's that have not been played for several weeks, or more.