I tried to use it once. I got nothing. I asked about it and they gave me a customer service gesture of 2,500 Rove Miles. I have not used them again. I'm just going to stick with AA shopping and Rakuten.
Supposedly the issue was I had put things in the cart one day, but didn't buy it. I came back the next day and some new items were in stock and I added it and made the purchase. But because I had items in the cart, it did not count. The whole time the Rove extension on Chrome was active, and every time I went to the site to browse it, the extension popped up to say the 6x bonus was active. So I didn't think I'd need to empty out the cart and put them all back in when it was already telling me it was active. It's too much of a hassle so I stopped using them.

TLDR: They are picky or user error, and I stopped using them after 1 attempt.