Its not great at all. Its about 50% the efficiency of charging with a cable.
Now, people buy these cars because they like to pretend that raping the planet for resources, refining lithium from lithium carbonate or lithium hydroxide (one of the most polluting and respurce intensive industrial processes known to man), building a car and shipping it halfway round a planet makes them somehow "green".
Well, using twice as much electricity to charge the damn thing is hardly a good thing in pursuit of a green goal, although it is jolly convenient.