I have several short cables and don't see a need to spend the money to have something with magnets. However, I was intrigued by this and have a few questions / comments.
REAL QUESTION!

Maybe I don't understand how this would work, but since it is attached to your keys, wouldn't using it be cumbersome since your keys are also still attached when using it? Or is the expectation that you unthread it each time you want to use it? How are you guys using it without your keys sitting as a pile between the two devices or do you just live with that?
MafSafe is certainly convenient, but it is also not efficient. If you often have access to power and you only need something like this in emergencies, then the loss of efficiency might work. However, for people who might need to go longer periods of time without power, wasting energy on wireless charging only shortens the time that someone can be mobile without power. Short cables for these things still have a wonderful place for powerless remote computing.