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Pros
Pro Free to download and use
It's completely free to download and use making for a good choice for those that do not want to purchase an emulator.
Pro Supports multiple Sega systems
Sega Mega Drive / Genesis and the Sega Master System are both supported seeing that ROMs for each play through the emulator.
Cons
Con Requires a good phone with high specs
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.