The MagSafe to MagSafe 2 Converter allows you to use the MagSafe connector on your LED Cinema Display, Thunderbolt Display, or MagSafe Power Adapter to charge your MagSafe 2-equipped Mac computer.
A Magsafe 2 adapter is not compatible with Apple computers that have a connector that normally uses "T" and "L" style MagSafe adapters.
I doubt it. If they planned to make it backwards-compatible, they would have released two converters. Anything new would have the MagSafe 2 included. Anything older would already have the older MagSafe adapter, so there would be no need to use a new MagSafe 2 with an old device.
The new MagSafe 2 is a 20V adapter instead of the old 17.5V, so a simple converter will not exist. It would have to down convert the voltage in order to be safe, and would not then be practical in size or cost.