Ads are bad and you are right! I know it, you know it and this is why I use less intrusive ads and I pick the location where they are shown very carefully.
Do not interrupt the user or he/she will quit the game/app.
What I try to say with the old version - I have App ver 1.xx and after few months I did write complete new version 2.00. I did add a button with a market link to the start screen of the old version which is telling a new version of the App is there but the users are not switching to the new version. The new version is not compatible with the old one.
In your case, you have big user base from WordHero and Anagram Hero. Did you try to move this user base to WordSearch Hero? Even 20% from them may be better than promoting with paid Ads?
I think better will be with big user base and IAP. The Ads may bring nothing… 0 income… Fill and Impression may be OK, but do they make money?
To keep developing games/app the developer needs income
Since WordSearch Hero is not doing that great, you could probably experiment with it a bit - different ads, different IAPs. Unless you don’t want to spend more time on it, which would be understandable.
Mind, I was going to write the same thing as Magnesus, but I decided you probably know about it…
On the other hand I have a different suggestion: maybe you should run more house-ads in your other apps to direct people to WordSearch Hero? The eCPM is low, but you get decent revenue with IAP, so the game has big potential, just needs the users. Is it monetising better (per DAU of course) than your other games? Maybe its worth it to direct people to this game instead of monetising them right away? The conversion could be higher than usual as its the right niche. I think you should compare the revenue per daily active users, and try it out if its better in WordSearch Hero.
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One more idea. You could show interstitials on exit (not every time, just sometimes), and every 3 - 5 games (count the games played by the player and don’t show it more often than once per 3 games, and not less often than every 5 games). That could boost your gross revenue from ads by ~20%. While with WordSearch Hero you get nice cash with IAPs, it could be nice for your games that monetise their users less. And I don’t think the users will leave your app due to some rare interstitials. Sure, nobody likes ads, but majority of the users will accept them.
sorry, couldn’t hold it