On the campaign map in Total War: Napoleon, an army is small enough to move across Europe with a finger. Enter a battle and that one piece becomes a row of unit cards, each waiting for separate orders. Feral's strategy game for iPhone and iPad keeps both scales, and the jump between them is where the size of your screen starts to matter.
Battles have a different pace. The campaign gives you time to weigh a trade agreement or decide which border needs an army. Once the fighting starts, several units can need attention at the same time. Look at Feral's mobile screenshots: the deployment panel lays out both armies side by side, but in battle that same strip of screen also has to hold the selected unit's orders. A player coming back from the PC version wrote in a US App Store review that pausing helped with touch commands.
The mobile edition has a reason for returning players to open the campaign map again. Spain, Portugal, Denmark and the Ottoman Empire are playable, so a border you remember crossing as France can become the one you have to defend. That changes the opening decision before you give a single order.
I'd pick the iPad for a first campaign if both devices are handy. On an iPhone, try a single battle before committing to Europe; you'll know quite quickly whether you can pick out the unit you mean.
