Nintendo has made it public that they in no way support this product as they feel it is disrespectful not only to them, but to all the other companies that have had their games pirated, and as a result of the many lawsuits from Nintendo, many sites like eBay and Amazon do not sell this flashcard. Now that doesn’t mean this product is just for illegal piracy; it is possible and perfectly legal if you own a physical copy of DS games and have backups of said games and wish to put them on the flashcard instead of carrying all your cartridges around. From what I heard, you can also somehow play SNES ROMs on it, but I believe even though they are obsolete ROMs it’s still a big deal with piracy.
As of right now, the R4s allow you to use your wi-fi to update it, and it seem to still be compatible and reliable. With each update that appears, there has been no problem whatsoever that has kept it from not working. One recommendation, you can order them with or without an SD card and I highly recommend getting one without one and buying an SD card at a store that sells them. For some reason the SD cards that come with the R4 3DS aren’t the best and instead of hasting with trying to get them to work, it’s better to just get one separately. These R4 3DS flashcards can go anywhere from $7 to $20 depending on where you buy the card. Now are these worth the money? Yes they are; if you’ve ever owned previous handheld systems before, you know it really isn’t fun carrying all your games with you when you go somewhere. From misplacing them, to switching from one cartridge to another, with this you never have to swap, you have all your games available to you at the touch of a button.