What's the use case? I could see potentially leaving old chargers at podiums for presentations or something. Most of our old ones are so tattered anyway it wouldn't be worth it.
Looks like since it has to convert from the old power spec to USB-C's power spec it requires a bigger MagSafe power adapter than the USB-C spec Apple power adapter. And it wouldn't properly charge a 15-inch MacBook Pro since there isn't a big enough MagSafe to accomplish 85W converted to USB-C.
This is an interesting one... but yea, just for old chargers. Yet most low power USB-C chargers are about as much as this adaptor (Looking at you Anker). Put that aside, how about this direction!
There are others like it, but you get the idea!
I use this magsafe-like adapter.
The advantage: it has enough connectors to let everything through (all kinds of data + power)
Disadvantage: the magnet is so strong that when you pull the cable, the adapter itself stays connected and the cable gets pulled out of the adapter or the adapter gets pulled out of the MacBook ;-)