I think the idea to do top up charges by plugging it in to your tablet is a novel one. The practicality of it though is a head scratcher.
And regular full charging of it was completely missed. This adapter seems like a "oops, here's an adapter cause when we designed this, we didn't think ti through fully"
When you're charging your tablet, why wouldn't that also be an opportune time to charge your pen? why not make it so both can be charged at the same time from the same powersource? even this solution is inelegant as you cannot charge the pen while charging the tablet. Unless you buy a 2nd set of power for the pen. This means you're only charging one thing at a time. Which will inevitably lead to situations where you get stuck with such an inelegant solution as a pencil sticking out of the bottom ofr your tablet for an indefined length of time, or plugged into the wall while you're using your tablet.
I'm not a fan of replacable AAA batteries like Microsoft went. Too much waste (although they claim 1 year out of 1 AAA battery), I would still rather a rechargable solution, but I'm not sure what Apple was smoking when they threw this together