Basically, BannerPlay is a way to advertise your eBay listings using banner ads placed on a variety of websites. The cool thing is that the app is integrated with eBay, so all you have to do is log into the app through the eBay website, choose the listing you want to promote, and work with the app to create an ad. You don't have to worry about formatting, design, etc. The app makes it easy.
You also don't have to worry about finding places to put your ad because BannerPlay sends it out through the different sites the company works with. Your ad is targeted using keywords as well as geography (if your shipping specifies US-only, your product will be shown to viewers in the US, etc). Through BannerPlay, a variety of viewers will see your ad.
In the ECommerceBytes interview, BannerPlay's product marketing manager says that as "a very rough estimate, each dollar in the daily budget buys about 10,000 views." That's a lot of eyes on your ad! The actual number can depend on your keywords, of course, and when you think about it, a smaller number of views could also work very well if you have a product that is targeted toward a very specific niche. After all, you just need one person to click through and buy your product.
This is a cost per click advertising system, and your account is only charged after someone clicks on your ad. You pay through PayPal. The cost you pay for a click depends on a bidding process, so price can vary, but it can be as low as a penny per click. As you will know if you've done Facebook ads or any other advertising with a bidding process, it can take a little experimenting to find the sweet spot in terms of what you need to spend to get a good return.
By the way, there is a BannerPlay app you can access through Etsy, too, with the same easy integration of using the images, keywords, etc from your listings. For online sellers on either platform (or both platforms), I think this is a tool worth trying. A lot of sellers express frustration about not getting enough views for their items from eBay's own search engine, so why not try bringing in some traffic from elsewhere?
Here's a video from BannerPlay with a brief overview of how it works.