I find it difficult to imagine a scenario where the above solution is more convinient than plugging the iPad into a charging cable. There probably are use cases for the product, but there are serious tradeoffs involved.
You either have to keep track of a third component, and plug it in/out as needed; or permanently mount it to the device for what has got to be an ugly/awkard lump on the iPad.
The only way I can see this working well is if the iPad/iPhone side is incorperated into a case. Which means there is probably a product out there that does this, at least for th iPhone. Less likely for the iPad. As long as you are doing a case, you might as well incorperate a battery in the case, and a passthrough lightning port. It would be a seriouls increase in the iPad/iPhone’s bulk, but the features and convinience might be worth it.
Now, does this product exist?
I don’t want to get into why the cable isn’t working out other than it isn’t. A flat surface charging station would be better for me.
Privately I can share but not publicly.