I haven't. Thanks for bringing it to my attention!
It reminds me of Booksends new release romance feature. Essentially, my take, it's a special single book Red Feather Romance promo blast. From what I read, I don't believe they promote it to their other email readers (freebooksy & bargainbooksy). They say it's for visibility and branding. I mean, $500 charge is gonna be tough to pay back with ROI and they warn you in their FYI section. It's pricey. But it might be worth it for those building press for a new release or ranking. Being that it's Written Word Media, it'll perform well. I've had good results with Red Feather Romance.
Let me know if you use this service.