Okay, the EZFlash-Vi is a DS-mode only Flash Cart. Since you have an original DS then you can easily upgrade the firmware properly. The kernals are easy to install too (just drop them on your SD card).
I personally LOVE the two that I've purchased. One for me and one for my wife. (Though we only currently have my 3DS, we plan to get a pair of DSi XLs in the future.) There are very few games that don't work on this card, and it works with a decent majority of homebrew. Personally, I find DS homebrew lacking compared to Wii and PS3, so I don't do a lot with it.
Something to note: If a DS game can communicate with a Wii game, it WILL work. I've done this with Batman The Brave and The Bold for the Batmite feature. Works flawlessly. If a game requires you to receive information through DS-Download Play, then it will NOT work, since the card is flashed to act like a certain game (Tak for older firmware, Guilty Gear for newer firmware.) All in all, the EZFlash-Vi is probably the easiest Flash Cart to work with, has great compatibility, and is still being supported faithfully.
Also, I made a nice Zelda skin for it.
For the price, EZFlash-Vi is a great choice. Just be sure you set it up the right way. Plenty of tutorials on that around here.
And something to think about, if you're looking into using Real-Time Save and Real-Time Guide, then understand that this card is far from perfect on that. If you just want to play your games the way they are on the DS, then this card is just fine.
Oh, and don't but it on that site you linked to. That's almost twice what I got mine for. I recommend Price Angels. You'll have to Google it though, since the Temp has a filter for that site for some reason. Their shipping is a bit slow, but its free and I've never had issues with them.