It's completely free to download and use making for a good choice for those that do not want to purchase an emulator.
Sega Mega Drive / Genesis and the Sega Master System are both supported seeing that ROMs for each play through the emulator.
Heavy usage on this one makes for slowdown on cheap phones that have low specs. A higher end phone is definitely recommended to use this app smoothly.
It supports the Xperia Play, Moga gamepads as well as HID gamepads. This way anyone can use the controller they like with the games in the emulator.
Depending on how one wants to hold their device this emulator will work wither way making for a convenient emulator as far as orientation goes.