lol. Aiming with a touchscreen device is a tough thing to do and all I own are touchscreen smartphones and tablets. I wouldn't buy the game if I don't have a controller that I can connect to a touchscreen smartphone or tablet.
I don't own iOS devices, but if I did, I may get this game.
I played Shadowgun, and Dead Trigger with a touchscreen, and they are both playable on touchscreen. Maybe, this game have auto-aim, or the enemies are slower, so you have more time to shoot.
I read a lot controller based first person shooters also come with auto-aim which helps you aim better when using joysticks, or directional pad which can be less accurate than keyboard and mouse for first person shooters.
A friend I have on Facebook shared this just last night and I have to admit it does look interesting however I read it was just on iOS devices which I now do not have. I am curious though to see how you would control the game on a touchscreen.