Yes, so they are quite different if they don't sell the same products. johnx was right to correct you and it was good of him to further define the difference.
Acekard 2i FTW. Although, I don't know if it's just me or it's a design flaw, but the acekard's contacts tend to shift. Barely half a millimetre in movement, but that somehow makes the difference between a non-functional flashcart and a flawless flashcart.
Im just gonna say DSTT coz well i had mine for a while now and i had no problems with it and it seems to work well with piracy protected games compared to others :S
in all fairness there isn't an m3 real i but there is an M3 Zero i but I really don't know much about it as I only have an m3 dsReal using Sakura. I'll recommend Acekard2i just because I have seen far more good reviews for it (and will likely get one if I ever get a DSi)
go for the m3i zero....I have had nothing but good things to say about m3 real and m3i zero. Plus it works on the dsi and has more features than any other dsi compatible card.
If you want one NOW I would go for Acekard 2i or CycloDS. I have an original R4 because I live in a small place called New Zealand lol. I would wait for the Supercard DSTwo though... GBA emulation!!