It depends on what you're using it for. It will be limited and might, probably won't, be as successful as their standard promo. If it's between deciding on Freebooksy/bargain books or ads, I'd go with the promotion first and foremost. The trouble with ads services is it takes time for books to take off with an advertisement. And Written Word Media, they only runs these for five days. I haven't done their Amazon ads service (but I'd be even more cautious cause it takes even longer for AMS to get cooking).

That being said, I'm using this service this week for Facebook ads for my new release. It's part of their New in Books Service promotion (which I recommend). For a new release, when you're not looking for ROI and more for ratings and extra visibility, it's a service that's worth it.

Another time I'd see a use this service is if you're running a special promo OR gunning for USA Today bestseller list/or any bestseller lists.

Finally, if you're already running your own ads, just do that. Usually you're your best promoter. I run Facebook ads through Written Word Media because I'm not on Facebook and don't run Facebook ads.

 

Beware of Reader Reach Facebook Ads, which is a complete scam. This service, which is supposed to help you sell your ebooks with custom-made ads, is almost completely ineffective.

I decided to pay $150 for an advertising campaign for my Thriller The New Guardians. Reader Reach Facebook Ads seemed to me to benefit from interesting feedback from authors. My Thriller has a 4.5/5 rating on Amazon, with ten reviews. Granted, that's a small number of reviews, and I had also decided not to lower the price of the ebook for this campaign. The price is $3.99, which is standard for a 432-page book. I really wanted to test the effectiveness of Written World Media's advertising team.
The ad campaign was spread over 5 days on Facebook. I thought that for this kind of service, Written World Media would only accept the challenge for ebooks likely to generate a return on investment.

My ebook was accepted, and as soon as the campaign was launched, I asked them to send me the advertising that had been set up. The advert read: "The New Guardians by Alan Spade is a great book to read. Highly recommend!"
I didn't get any link to the ad on Facebook.

By the end of the first day, I had made only one sale. I knew I needed to sell 112 ebooks over the 5-day period to recoup my investment. Sensing disaster, I immediately emailed Written World Media.
Hi,
The image is good, but the text... Did you ask an 8-year-old to write it? It's so boilerplate. So dull. One sale so far. If it stays that way, I don't predict much more.

Best,
Alan
Here's the boilerplate answer from Written World Media:

Hi Alan,

Thanks for getting back to us! Because Facebook provides a limited amount of space for text, our team uses an excerpt from a five-star review. The campaigns start small and build over time, therefore you’ll likely see more consistent visibility for your book across multiple days and not a single-day spike. We have an article on our website that you may be interested in about what to expect with the ads; you can click here to check it out!

Let me know if you have any other questions!

All the best,

I only sold four ebooks in all by the end of the fifth day. 4. Ebooks. That's 1/28th of the number of ebooks that would have needed to be sold for ROI.
I had no access to statistics on cost per click, number of impressions, or which ad would have performed best. Nothing.
If anything, it wouldn't have mattered too much if I'd sold more ebooks. But the result is absolutely abysmal. This service is to be avoided! The only advantage for me in using this service is that it allows me to warn other authors of the scam.