I suggest not getting the R4 and if you already have one, you really should think about getting a new flashcard, there are plenty of flashcards out there that are far cheaper and have better support, compatibility and features. The R4 has stopped being manufactured which means that it has reached the end of its life. You can expect only minor updates if any at all from the R4 team though right now, it doesn't look promising.
Several games, even some that came out over a year ago don't work on the R4. Also many newer games coming out have problems on the R4 either not running the game at all or the game is extremely buggy and freeze often. Also games with the new save type are not supported on the R4 so any games coming out with the new save type will not save. Also there are a few homebrew apps that have trouble on the R4 as well.
The R4 overall, is extremely limited and buggy. The cheat system has many flaws and can cause games to freeze or simply nt work when using cheats on some games. Also a few cheat types are not supported leaving you with a good many cheats not working on the R4. Also the R4 limits the number of cheats and games that gets displayed on the cheats page.
So basically, the R4 is on life support and has been for quite a long time now. Many newer flashcards have surpassed the R4 in many ways, including compatibility. The R4 is showing its age, thanks to hardware limitations (The R4 Firmware not being flashable), features like SDHC support and many others can never be added. The R4 was a fine cart when it first came out, but now its just an old, over prices flashcard.
The R4 has many clones as well, some supporting SDHC cards, these are not enhanced R4s nor improved, they simply had the hardware added to support SDHC cards while the loader/firmware they use is the exact same as the real R4DS byte to byte. This means that the clones have the same problems of the real R4DS and if the R4DS stops getting updated, so will the clones. So the R4 Upgrade V2, N5, R4DS III and so on are just all cheat knockoffs and should be avoided at all costs as the R4 Team is planning one last update that will brick the clones and possibly the DS that they are on.