I repaired a few scratched CD's out of my collection before I burned the lot to mp3. I used the motorized version and achieved OK results.
The machine removed the shiny surface on the CD, and left a machined finish from the circular pads and supplied abrasive paste.
This method only works for light scratches on the underside of the CD.
I had a Sisters of Mercy CD single (More) which pieces of the printed layer had de-laminated from the surface. After using the CD resurfacing machine I could see through the plastic when I held it up to the light.
When ripping my CD's to mp3 format I found that there was variation from different CD and CD/DVD drives as to how they picked up scratches on the surface of the CD during ripping.
My modern Asus 32x CD/DVD had trouble with scratched CD's but my older CD/R drive had no problem with the same disk. I ended up replacing about 5 CD's in my collection with ebay purchases.