anyone with experience of the "CD lathe"

I've been using one for the past few months, and all I can say is, I can't imagine myself doing without it. The link below will take you to reviews on the Audio Desk Systeme website -- I took the plunge after reading Richard Foster's review in HiFi+, and I've found his comments to be completely accurate.

http://www.audiodesksysteme.de/index.php?kat=10_23

The operating principle seems sound

Why? The principal physics of operating principle is claimed to be similar to the well known green felt tip pen scam? The description claims that "Light scatter is often to blame for poor sound potential. Light scatter moves randomly through CDs and audibly deteriorates reproduction." I have not read anything like this in AES papers...surely manufacturers would try to deal with this problem if it were real.

Yes, and the improvements to the quality of music reproduction is significant. I do not need to know all the physics. This tool is the real deal. My problem is finding the time to cut the cds.

I have had one for three years. I used it on all cds and sacds that I could find the time to cut. I found that blackening the outer edge also helped. Presently I copy all redbook onto black cdrs using the RealityCheck burner and have found that black cdrs seem to gain no benefit from having the AudioDeck trimming.

If you buy a used one that has been heavily used, you may need to buy a new cutting head.