Gemini has a nice clean interface that makes setting up any campaign a breeze. Even though Gemini is relatively new, I’ve already ran quite a few successful campaigns on it. It is quite easy to get clicks for .05 CPC in the US for Display. Yahoo inventory is usually an older audience, which means they have more money and frequently purchase.
So far Yahoo is following in the steps of Google in the sense that they’re very picky on what they allow. Also, if you plan to run search campaigns on Gemini, the CPC is quite expensive for both mobile and Desktop inventory.
Gemini still isn’t known by many advertisers so that alone has it’s advantages. If you’re already successfully running on Google & Bing and want to expand your traffic I highly suggest trying out Gemini.