It's been noted in other topics (cba to find links) that yes, it does indeed work, also with flash cards that did not EVER have any 3DS support (R4 Revolution for DS, for example, all the old crap).

But then you have the cart sticking way out like a PassMe. No bueno.

Edit - you'd be better suited spending your money, however, on something that DOES natively work on the 3DS, like the R4i Gold from r4ids.cn or the Supercard DSTWO.

 

Yeah I'm not much one to cheat in games, but from what I have heard (Rydian mentioned it at one point, THAT much I do know, but I can't find the post/topic), as long as you have the AR you could use that to launch the flashcart. I could theoretically use one, should I get one, to boot my old iTouchDS RTS, my original R4, or my brother's now-blocked Acekard 2i.

The only downside with it is that it's plain bulky :/

Edit - yes, exactly what the video shows, which I didn't watch until now. It's a process, and as you can see it does stick out quite a bit. If you already have an older flashcart and you already have an AR 3DS, it's a cheap solution if you don't want to drop a few bones on a new card just yet, but in the long run it's still a pain in the ass. XD