I never buy books with my Kobo. It's just too slow and hard to type. I prefer to use my laptop and download books to my device over wifi. (I never use the desktop application. It's evil.
) I did, once, buy a book with my phone when I didn't have access to my computer. It worked well and I would do it again in the same situation.
I don't find Kobo's recommendations particularly useful. Recommendations for books by my favourite authors are almost always for books that I've already read. Other recommendations usually don't appeal to me and I have never bought a book on that basis.
For what it's worth, I use Goodreads to keep track of books I've read and books I want to read, and their recommendations are even wackier!