I ordered two different flashcards from
NDS-Card.com (outstanding service and follow up, by the way) and got them a couple of days ago.
Do note that I always play the games as if I were using a cartridge in its original console. This is, no cheat codes, no Real Time Saving, no extra features. I only tried these features once, to check if they indeed work, but did not do an extensive test.
The
R4i GOLD Card r4ids.cn works with the vanilla Wood kernel (2013), has a simple yet functional menu interface and it is fast and responsive when loading DS games and when going back to the menu. As a plus, this card can be used to install custom firmware on a 3DS.
The
r4i-SDHC r4i-sdch.com works with its own, more recent firmware (2016), has a richer menu and is slow at loading DS games when compared to the Gold card. It seems that a save sate is created when a game is loaded and this is the reason why it takes more time. This card
cannot be used to install custom firmware on a 3DS.
Because I do not use most of the extra features, I prefer the YSMenu firmware, whose menu is simpler and loads games faster (1).
I think that the
R4i GOLD Card r4ids.cn is the better option. But if you use the extra features, you may want to try different menus until you find the one which suits you best.
(1) I used this version of YSMenu and set it as the primary menu.
https://gbatemp.net/threads/retrogamefan-updates-releases.267243/
https://gbatemp.net/threads/how-to-install-ysmenu-woodr4-on-r4i-sdhc-3ds-rts.470619/