The EZFLASH 3 IN 1 is a accessory for the Nintendo DS that has 3 functions, rumble, GBA, and extra ram for the Nintendo DS. This is very convenient, I don't have to switch to a ram pack, when I want to use the DS browser, or when I want some rumbling action, and even when I want to play a GBA game.
The EZ part, is only EZ when you have the company's EZFlash slot-1 card, without it, its going to take some time to get it working. You need to download a extra program to put on your DS, I'm not going to explain it in great detail, but its called the Rudolph 3in1 tool, google it.
The RAM, is self-explanatory, it justs a extra boost of power for the DS to the web browser. Also many homebrew developers have implemented it into their programs, for example, the Snemulds, can use the extra RAM to allow greater compability of SNES games. A great add-on for people.
The rumble has 3 level of intensity, High, Medium, and you guessed it, Low. High is on par with the official rumble pack. It is very loud like the official one when it is in high, making it very distractiing when playing games like Elite Beat Agents where you need to listen to the rhythm. Medium is quieter but still loud. Low is nearly 100% quiet, it still has feeling of vibration but now very powerful.I usually use medium, since it nearly has the power of High and almost the quietness of low, I also use headphones making it harder to hear the rumble
GBA support is well GBA support, you no longer need to switch game carts when wanting to play a new game.
The EZFlash is a very nice add-on for your DS, I don't recommend it for one reason. You will barely use it. I have it but it just sits there inside my DS. I only use it when I want to surf the web on my DS, I don't have alot of games that uses rumble and I don't like most GBA games. But if you're the opposite of me, then go ahead and get it, it will save you money.