Cartel Kings is a portrait one handed shooter for Android that is free to play and includes in app purchases that range from $4.99 - $99.99 per item.
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Pro One handed portrait gameplay
Cartel Kings is played in portrait mode making for a shooter that can be played one handed. Being that most shooters play in landscape, this is a bit of a change for the genre on Android, allowing for easy play when only having one hand free.
Con Pushes too much for in-app-purchases
There is quite a lot of difficulty spike in the game that tries to force the player into spending real money on in-app-purchases in order to progress. The amount of grinding it would take to complete any section of the game is too much for non paying players.