The converter works as advertised. It lets me use an existing power supply with my new MacBook Pro Retina.
The converter's magnet attaches to the power supply's old MagSafe connector very effectively. The magnetic connection between the converter and the MacBook isn't as strong. The problem is that the old MagSafe adapter and the converter is now long enough that leverage makes it very easy to disconnect from the MacBook. This is very annoying, especially if you hold the MacBook in your lap while using it.
The Adapter that came with my Thunderbolt Display worked for about 4 months. Did what it was supposed to do, but then suddenly I noticed my MBP Retina wasn't charging anymore when connected to the Display. Luckily I had a spare adapter and it works again.
Postitive - It does what it's supposed to.
Negative - Dies after a while.