There is a ton of ongoing discussion over at the Acoustic Guitar Forum, where a new thread pops up every few days. Comments range from "really makes a difference" to "complete waste of money, does nothing at all". Want to start an on-line fight? Mention the Tone Right device...
Personally I put it in the same category as late night commercials for weight loss pills and workout infomercials, and copper bracelets to cure arthritis pain. In other words: don't bother, just play your guitar.