A Supercard DSTwo is your best choice for a DS flashcard. It's one of the only working DS flashcards that still work on 3DS' latest firmwares. It also has built in CPU, which helps you to emulate GBA and SNES games nicely. You can't emulate GBA games on other flashcards without this extra CPU power.
You wouldn't be wrong for getting it, and it surely does not brick your 3DS. Only a 3DS flashcard such as a Gateway or R4i 3DS Gold Deluxe can actually brick your 3DS. But only if it's a clone. If you shop from trusted sources, you''ll be fine.
Just remember the difference between a DS flashcard, and a 3DS flashcard. They're both entirely different. You would need a 4.5 3DS to play a 3DS flashcard. So that's not an option.
The DSTwo features free cheats for DS games, simple to use. Im not sure about pokegenning, maybe someone else will answer that :c
So basically, your DSTwo can play DS, GBA, GB, SNES, NES, Sega genesis.
You won't be able to play 3DS roms on it, unless you bought a used 3DS from ebay that had 4.5 on it, then bought a Gateway.
Also to clear a confusion for you, there's an R4i Gold 3DS (DS flashcard), then there's the R4i gold 3DS Gold Deluxe (3DS flashcard). From the same manufacturer, but different functionality.