Ansich the Magsafe Keeper is a great idea to prevent that you lose the little adapter from old to new Magsafe. This way you can easily hang this on an old power supply or the Apple Thunderbolt Display, to be prepared for each device.
The only complaint is the price: 12.90 is too much for a band with a piece of rubber. This makes it even more expensive than an Apple Magsafe on Magsafe 2 Converter, which has an MSRP of 10.
