Most of my Kobo sales come from their promos or my BB ads too. No disagreeing here.
So far, to report regarding "sponsored" ad results, I have seen an uptick from my older sci-fi title Candy Savant. Since this occurred around the same time as these mysterious ads, and hardly at all before, I believe I can attribute it to it (I also haven't been advertising this title at all recently). But I don't know. It's not much, but it's something.
The current sponsored ads are mainly duplicates with series. The true test, of course, is whether they'd be connected with authors or other keyword/books outside of our normal search. They might just be collecting clicks at this point. ??