I avoided buying the DSI due to its pitiful battery life compared to the DSlite (which lasts me from 10-15 hours), but my sister's uses Acekard.
Avoid R4 for three reasons-
-its almost always never updated enough for newer game releases and homebrew.
-competitors' like M3 REAL and Acekard are regularly updated and have more functions
-its currently illegal to have an R4, as its being heavily sued against and taken away from stores, soon you wont even have any support
Do you use it to play old roms? Like from old Gameboys, GBA or even SNES?
There is no way to emulate the GBA on the DSI, but for gameboy/gameboy color use Lameboy, and snesDS for SNES emulation. snesDS runs on the DSlite overclocked, but should run without overclocking in the DSI due to its superior RAM.
Now, its legal to have emulators, however the legality of each rom varies, as some game companies no longer exist, while some got sold to others and some are still selling the roms in console stores and in game compilations.
Or you could say f*ck you to laws that go against consumer rights and are in legally gray areas (yes DVD regions, Im looking at you) and enjoy playing ROMs of games you have already bought, thankfully the game companies there havent started a witch hunt ala RIAA's. Yet.